NEUROANATOMYNEUROANATOMY THESKULL1,2 1. Describethekeyfeaturesofthebonesoftheskull* 2....

NEUROANATOMY THE SKULL1,2

1. Describe the key features of the bones of the skull 2. Identify the main skull bones on AP and lateral X-‐rays, identifying the normal appearance of sutures and pituitary fossa and the upper cervical spine

CHAPTER 7 • HEAD 487

FIGURE 7.1. A and B. Adult cranium (skull). In B, the pterion is the area of junction of four bones within the temporal fossa.

Nasion

Superciliary arch

Supra-orbitalnotch

Superior orbitalfissure

Inferior orbitalfissure

Zygomaticofacialforamen

Piriformaperture

Inferiorconcha

Intermaxillarysuture

Alveolar processof maxilla

Angle of mandible

Mental foramen

Mental tubercle(A) Anterior viewMental protuberance

Mandibular symphysis

Mandibular tooth

Vomer

Perpendicularplate of ethmoid

Infra-orbitalforamen

Middle concha

Optic canal(foramen)

Supra-orbitalmargin

Glabella

Calvaria

Nasalseptum

Inferior andsuperiortemporal lines

Temporal fossa

Squamous partof temporalbone

Lambdoidsuture

Zygomatic arch

External occipitalprotuberance

Orbitomeatalplane

External acousticmeatus

Mastoid process

Styloid processOf mandible

Head

Ramus

Angle

Body

Mental foramen

Mentalprotuberance

Alveolar processof mandible

Coronoid process

Anteriornasal spine

Piriformaperture

Crest oflacrimal bone

Nasion

Pterion

Coronal suture

(B) Lateral view

EthmoidFrontalLacrimalMandibleMaxillaNasalOccipitalParietalSphenoidSuturalTemporalVomerZygomatic

Bones:

EthmoidFrontal

LacrimalInferior conchae

MandibleMaxillaNasalParietalSphenoidTemporalVomerZygomatic

Bones:

Moore_Ch07.indd 487Moore_Ch07.indd 487 1/15/14 2:26 AM1/15/14 2:26 AM


FIGURE 7.1. A and B. Adult cranium (skull). In B, the pterion is the area of junction of four bones within the temporal fossa.

Nasion

Superciliary arch

Supra-orbitalnotch

Superior orbitalfissure

Inferior orbitalfissure

Zygomaticofacialforamen

Piriformaperture

Inferiorconcha

Intermaxillarysuture

Alveolar processof maxilla

Angle of mandible

Mental foramen

Mental tubercle(A) Anterior viewMental protuberance

Mandibular symphysis

Mandibular tooth

Vomer

Perpendicularplate of ethmoid

Infra-orbitalforamen

Middle concha

Optic canal(foramen)

Supra-orbitalmargin

Glabella

Calvaria

Nasalseptum

Inferior andsuperiortemporal lines

Temporal fossa

Squamous partof temporalbone

Lambdoidsuture

Zygomatic arch

External occipitalprotuberance

Orbitomeatalplane

External acousticmeatus

Mastoid process

Styloid processOf mandible

Head

Ramus

Angle

Body

Mental foramen

Mentalprotuberance

Alveolar processof mandible

Coronoid process

Anteriornasal spine

Piriformaperture

Crest oflacrimal bone

Nasion

Pterion

Coronal suture

(B) Lateral view

EthmoidFrontalLacrimalMandibleMaxillaNasalOccipitalParietalSphenoidSuturalTemporalVomerZygomatic

Bones:

EthmoidFrontal

LacrimalInferior conchae

MandibleMaxillaNasalParietalSphenoidTemporalVomerZygomatic

Bones:


Figure 1 (above) and 2 (below) show the bones of the skull2

Year 3 -‐ Neuroanatomy

Safah Sharif 2

I wasn’t able to find any decent images of skull x-‐rays but I would recommend going through this tutorial as it’s quite useful: http://www.radiologymasterclass.co.uk/tutorials/ct/ct_brain_anatomy/ct_brain_anatomy_start


FIGURE 7.3. Cranial base. (continued) B. Cranial fossae of internal surface of cranial base. C. Lobes and cerebellum of brain related to cranial fossae. D. Features of internal surface.

(B) Superior view, cranial fossae (C) Inferior view of brain

Occupiesanterior fossa

Occupiesmiddle fossa

Occupiesposterior fossa

Anterior fossa

Middle fossa

Posterior fossa

Frontal lobe

Temporal lobe

Cerebellum

Groove fortransverse sinus

Internal occipitalcrest

Groove forsigmoid sinus

Clivus

Internal acoustic meatus

Foramen lacerum

Foramen spinosum

Posterior clinoidprocess

Hypophysial fossa*

Anterior clinoid process

Optic canal

Prechiasmatic sulcus

Tuberculum sellae*

Posterior ethmoidalforamen

Cribriform plate

Crista galli

Foramen cecumFrontal crest

Anterior ethmoidalforamen

Orbital part of frontalbone (orbital plate)

Lesser wing of sphenoid

Sphenoidal crest

Superior orbital fissure

Greater wing ofsphenoid

Foramen rotundum

Foramen ovale

Groove for middlemeningeal artery

Dorsum sellae*

Petrous ridge

Jugular foramen

Hypoglossal canal

Foramen magnum

Cerebellar fossa

*Components of sella turcica

(D) Superior view, internal surface of cranial base

FrontalSphenoidEthmoidParietalTemporalOccipital

Bones:


Figure 3 -‐ The foramina of the skull2


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CRANIAL NERVES3,4,5 1. Identify and name the cranial nerves observed on the surface of the human brain 2. Discuss the course of the cranial nerves and their distribution, concentrating on loss of

function if damaged

Figure 4 -‐ Cranial nerves as seen on the surface of the brain3


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NERVE FUNCTION COURSE

I: Olfactory Special somatic sensory Olfaction

• Olfactory neurones in roof of nasal cavity • Pass through cribiform plate of ethmoid

bone to olfactory bulb on frontal lobe • Information processed in bulb, then pass

to olfactory tract II: Optic Special sensory

Vision • Optic fibres join at optic disc • Enter skull via optic canal, then decuss • Most nerves project to lateral geniculate

body of thalamus • Some fibres enter pre-‐tectal nucleus

(pupillary light reflex) & suprachiasmatic nucleus (circadian rhythm)

III: Oculomotor Somatic motor Innervation of 4 extraocular muscles

Parasympathetic Contraction of pupillary smooth muscles

• Exit at brainstem and leaves skull via the superior orbital fissure

• Parasympathetic fibres derived from Edinger-‐Westphal nucleus, run alongside motor nerves

IV: Trochlear Somatic motor Innervates superior oblique muscle

• Emerge from posterior aspect of midbrain

• Run with Oculomotor through cavernous sinus

• Leaves skull via superior orbital fissure V: Trigeminal Somatic sensory

Touch, pain, proprioception, temperature of face, mouth, nasal passages, anterior

2/3 tongue Branchial motor

Muscles of mastication

• 3 divisions: o V1: ophthalmic o V2: maxillary o V3: mandibular (carries motor)

• Exit skull via foramen ovale • Attaches to pons via sensory trigeminal

ganglion VI: Abducens Somatic motor

Innervates lateral rectus • Emerge from ponto-‐medullar junction • Exit skull via superior orbital fissure

VII: Facial Branchial motor Muscles of facial expression, stapedius &

digastric muscle Special visceral sensory Taste -‐ anterior 2/3 tongue

• Passes through internal acoustic meatus to facial canal and middle ear, then branches off

VIII: Vestibulocochlear Special somatic sensory Hearing & balance

• Passes through internal acoustic meatus to middle ear, then divides (into vestibular & cochlear)

IX: Glossopharyngeal Somatic sensory Sensation to middle ear, pharynx &

posterior 1/3 tongue Branchial motor

Innervates stylopharyngeus Parasympathetic

Stimulates parotid gland

• Motor component arises from nucleus ambiguous

• Sensory fibres pass through nucleus ambiguous & hypoglossal

• Exit via jugular foramen

X: Vagus Branchial motor Innervates muscles of pharynx & larynx

(speech/swallow) General somatic sensory

Sensation to pharynx & meninges General visceral sensory

Chemoceptors & baroceptors in aorta Special visceral sensory

Taste from epiglottis & pharynx Parasympathetic

Innervation to heart, lungs & GIT

• Motor arises from nucleus ambiguous • GSS fibres end in trigeminal sensory

nucleus • GVS ends in nucleus solitarius • PS arises from dorsal motor nucleus of

vagus • Originates from medulla and exits skull

via jugular foramen • Passes into carotid sheath then enter

thorax • R à posterior vagal trunk


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• L à anterior vagal trunk o Gives off L recurrent laryngeal

which hooks under arch of aorta • Enter abdomen via oesophageal hiatus in

diaphragm XI: Accessory Branchial motor

Innervates SCM & upper part of trapezius • Emerges from anterior horn of spinal

cord (C1-‐C5) • Enters skull via foramen magnum then

exits again via jugular foramen XII: Hypoglossal Somatic motor

Intrinsic muscles of tongue • Originates at hypoglossal nucleus &

emerges from medulla • Exits skull via hypoglossal canal

Figure 5 -‐ The course of the vagus nerve (CNX)6


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THE BRAIN1,2 1. Describe the general layout of the cranial cavity and the meninges 2. Identify the principle parts of the brain including the cerebral hemispheres, cerebellum,

diencephalon, midbrain, pons and medulla oblongata and discuss their functions 3. Describe the location, internal organisation and blood supply of each main area of the

cerebral cortex that is considered to have a particular function in relation to motor control, sensory perception, initiation and control of speech, the intellect and expression of emotion, stating function an clinical significance of each

4. Identify the components involved in the production and flow of cerebrospinal fluid including the location of the ventricles

5. State the names and major components of the basal ganglia and describe their shape, relative position and clinical significance

6. Describe the form, location and fibre content of the internal capsule of the forebrain and state its function and clinical significance describe the position, function and clinical significance of the Subthalamic nucleus and the substantia nigra

7. Recognise the main gross features of the brain on CT and MRI scans 8. Describe the general form and arrangement of the principal parts of the brain and brainstem 9. Describe the main structural and functional features of the brain and the brainstem 10. Describe the location and relations of the pituitary gland Meninges The brain is enclosed in 3 layers of membraneous connective tissue: Extradural: no natural space, however, ruptured meningeal arteries can push periosteum away from

the cranium (extradural haemorrhage) Dura mater: tough, thick external fibrous layer

• Adheres to internal surface of the cranium • 2 layers: external periosteal & internal meningeal (IM) • IM layer: at foramen magnum, is continuous with spiral cord dura • Infoldings of IM divide the cranial cavity into compartments

o Falx cerebri -‐ lies in longitudinal cerebral fissure, separating L& R hemispheres o Tentorium cerebelli -‐ separates occipital lobes from cerebellum o Falx cerebelli -‐ partially separates cerebellar hemispheres, inferior to tentorium

cerebelli o Diaphragma sellae -‐ covers pituitary gland in hypophysial fossa

Subdural: no natural space -‐ created when blood gathers between the dura & arachnoid following

trauma Arachnoid mater: thin intermediate layer

• Avascular • Held against dura by pressure from CSF

Separated by subarachnoid space -‐ contains CSF (contains cerebral veins that drain into superior

sagittal sinus)

Pia mater: delicate internal vascular layer • Highly vascularized -‐ very fine vessels • Adheres to surface of brain


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Arterial Supply2

• Brain receives ~1/6 of cardiac output • Supply is from internal carotid & vertebral arteries

Figure 6 -‐ The meninges covering the brain2

Figure 7 -‐ Inferior view of the brain, showing the Circle of Willis2


Frontal lobe

Anterior cerebral artery*

Anterior communicating artery*

Anterior cerebral artery*

Middle cerebral artery*

Posterior communicating artery*Oculomotor nerve (CN III)

Trigeminal nerve (CN V)Basilar artery

Labyrinthine artery

Anterior inferiorPosterior inferior

Cerebellararteries

Vertebral arteryAnterior spinal artery

Hypoglossal nerve (CN XII)Spinal accessory nerve (CN XI)Vagus nerve (CN X)

Glossopharyngeal nerve(CN IX)

Vestibulocochlear nerve(CN VIII)

Facial nerve (CN VII)Abducent nerve (CN VI)

Superior cerebellar artery

Posterior cerebral artery*

Internal carotid artery*Temporal lobe

Optic nerve (CN II)

Corpus callosum

Olfactory bulb and tract

(D) Inferior view

Trochlear nerve (CN IV)

* Components of cerebralarterial circle (of Willis)

FIGURE 7.13. Arterial supply of cerebrum. (continued) D. Cerebral arterial circle and cranial nerves.

Vasculature of BrainAlthough it accounts for only about 2.5% of body weight, the brain receives about one sixth of the cardiac output and one fifth of the oxygen consumed by the body at rest. The blood supply to the brain is from the internal carotid and vertebral arteries (Fig. 7.13; Table 7.2).

The internal carotid arteries arise in the neck from the common carotid arteries and enter the cranial cavity with the carotid plexus of sympathetic nerves through the carotid canals. The intracranial course of the internal carotid artery is shown in Figure 7.14. The cervical part of this artery ascends to the entrance to the carotid canal in the petrous temporal bone. The petrous part of the artery turns horizontally and medially in the carotid canal to emerge superior to the foramen lacerum and enters the cranial cavity. The cavernous part of the artery runs on the lateral side of the sphenoid in the carotid groove as it traverses the cavernous sinuses. Inferior to the ante-rior clinoid process, the artery makes a 180-degree turn to join the cerebral arterial circle. The internal carotid arteries course anteriorly through the cavernous sinuses,

with the abducent nerves (CN VI) and in close proximity to the oculomotor (CN III) and trochlear (CN IV) nerves. The terminal branches of the internal carotids are the anterior and middle cerebral arteries (Fig. 7.13C,D; Table 7.2).

The vertebral arteries begin in the root of the neck as branches of the first part of the subclavian arteries, pass through the transverse foramina of the first six cervical vertebrae, and perforate the dura and arachnoid to pass through the foramen magnum. The intracranial parts of the vertebral arteries unite at the caudal border of the pons to form the basilar artery. The basilar artery runs through the pontocerebellar cistern (Fig. 7.12B) to the superior border of the pons, where it ends by dividing into the two posterior cerebral arteries.

In addition to supplying branches to deeper parts of the brain, the cortical branches of each cerebral artery supply a surface and a pole of the cerebrum. The cortical branches of the:

• Anterior cerebral arteries supply most of the medial and superior surfaces and the frontal pole.



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INTERNAL CAROTID ARTERIES • Arise in neck from common carotid arteries • Enter cranial cavity via carotid canals, along with

carotid plexus of sympathetic nerves • Terminal branches: anterior & middle cerebral

arteries VERTEBROBASILAR ARTERY

• Vertebral artetries begin in root of neck as branches of first part of subclavian arteries

o Pass through transverse foramine of the first 6 cervial vertebae o Perforate dura & arachnoid to pass through foramen magnum o Unite at caudal border of pons to form basilar artery

• Basilar artery o Runs through pontocerebellar cistern to superior border of pons o Divides into terminal branches: posterior cerebral arteries

Cerebrum7

The cerebrum is split into 2 hemispheres, left and right, by the longitudinal fissure Each hemisphere is split into 4 lobes which have several functions: 1. FRONTAL -‐ supplied by MCA & ACA

• Personality • Reading • Problem-‐solving • Long-‐term plans • Pre-‐motor cortex (at border of central

sulcus)

• Executive functions • Retaining long-‐term memory • Some emotion • Social etiquette

2. PARIETAL -‐ supplied by MCA

• Orientation • Sensory cortex (at border of central

sulcus)

• Spatial sense • Navigation

CIRCLE OF WILLIS Anastomsis of thw following arteries

• Posterior cerebral • Posterior communicating • Internal carotid • Anterior cerebral • Anterior communicating


BRAIN

The following is a brief discussion of the parts of the brain, vasculature, and ventricular system because the brain is usu-ally studied in neuroscience courses. The brain is composed of the cerebrum, cerebellum, and brainstem (midbrain, pons, and medulla oblongata) (Fig. 7.11A,B). Of the 12 cranial nerves, 11 cranial nerves arise from the brain (Fig. 7.11C). They have motor, parasympathetic, and/or sensory functions. Generally, these nerves are surrounded by a dural sheath as they leave the cranium; the dural sheath becomes continu-ous with the connective tissue of the epineurium. For a sum-mary of the cranial nerves, see Chapter 9.

Parts of BrainWhen the calvaria and dura mater are removed, gyri (folds), sulci (grooves), and fissures (clefts) of the cerebral cor-tex are visible through the delicate arachnoid–pia layer. The parts of brain include (Fig. 7.11A,B)

• The cerebrum includes the cerebral hemispheres, which form the largest part of the brain and are separated by a longitudinal fissure into which the falx cerebri extends. Each hemisphere is divided into four lobes: frontal, parietal,

temporal, and occipital. The frontal lobes occupy the an-terior cranial fossa, the temporal lobes occupy the lateral parts of the middle cranial fossae, and the occipital lobes extend posteriorly over the tentorium cerebelli (Fig. 7.3B).

• The diencephalon is composed of the epithalamus, thal-amus, and hypothalamus and forms the central core of the brain (Fig. 7.11B).

• The midbrain, the rostral part of the brainstem, lies at the junction of the middle and posterior cranial fossae. CN III and IV are associated with the midbrain.

• The pons, the part of the brainstem between the mid-brain rostrally and the medulla oblongata caudally, lies in the anterior part of the posterior cranial fossa. CN V is associated with the pons.

• The medulla oblongata (medulla), the most caudal part of the brainstem, is continuous with the spinal cord and lies in the posterior cranial fossa. CNs IX, X, and XII are associated with the medulla, whereas CN VI to VIII are located at the junction of the pons and medulla.

• The cerebellum is the large brain mass lying posterior to the pons and medulla and inferior to the posterior part of the cerebrum. It lies beneath the tentorium cerebelli in the posterior cranial fossa and consists of two hemi-spheres united by a narrow middle part, the vermis.

Lateralsulcus(fissure)

Pons Pons

Medulla (oblongata)

Transversefissure

Postcentral gyrus Precentral gyrus

Central sulcus

Occipitalpole

Frontal pole

Temporal pole

Choroid plexus

Parieto-occipitalsulcus (fissure)

Pineal body(epithalamus)

Calcarinesulcus

Cerebralaqueduct

4th ventricleHypothalamus

Thalamus

Midbrain

Medulla (oblongata)Median aperture

Central canal

Septumpellucidum

Corpuscallosum

(B) Medial view(A) Lateral view

Cerebellum

Optic nerve (CN II)

Oculomotor nerve(CN III)

Trochlear nerve(CN IV)

Trigeminal nerve(CN V)

Abducent nerve(CN VI)

Facial nerve(CN VII)

Hypoglossal nerve(CN XII)

Glossopharyngealnerve (CN IX)

Vagus nerve (CN X)

Spinal accessorynerve (CN XI)

(C) Inferior view

Cerebellum

Vestibulocochlearnerve (CN VIII)

Lobes and structures

Frontal lobeParietal lobeTemporal lobeOccipital lobeCerebellumDiencephalon

Brainstem: Midbrain Pons Medulla (oblongata)

FIGURE 7.11. Structure of brain. A. Right cerebral hemisphere, cerebellum, and brainstem. B. Parts of brain identified on median section. Arrow, site of interventricular foramen. C. Brainstem and cranial nerves.


Figure 8 -‐ Lobes of the brain2


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3. TEMPORAL -‐ supplied by MCA• Short-‐term memory • Auditory processing

• Primary auditory cortex • Hippocampus

4. OCCIPITAL -‐ supplied by PCA

• Primary visual cortex

12

Seminar Seminar Seminar Seminar TwoTwoTwoTwo Class ActivitiesClass ActivitiesClass ActivitiesClass Activities

Use the illustrations below to colour and label the following functional regions of the brain: Sensory, motor, visual, speech, personality, emotion, memory, hearing, taste, spatial ability.

Figure 9 -‐ Functional areas of the brain


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Ventricles8,9 • Hollow, fluid-‐filled cavities in the brain which produce & transport CSF • CSF made in choroid plexus -‐ collection of specialised epithelial cells in the ventricle lining

o Plasma filtered from blood to form CSF • 2 lateral ventricles -‐ right & left

o One in each hemisphere o Lateral ventricle volume increases with age o Connect to 3rd ventricle via foramen of Munro

• 3rd ventricle o Lies between right & left thalamus o Connects to 4th ventricle via aqueduct of Sylvius

• 4th ventricle o Lies between pons & medulla oblongata in the brainstem o Srains into subarachnoid space (recycled back into circulation) & spinal cord

CEREBROSPINAL FLUID • Clear, colourless liquid containing ions, glucose, proteins, urea & lymphocytes • Protection: absorbs shock to limit neural damage • Nutrition: provides glucose; maintains chemical balance • Buoyancy: prevents excess pressure on base of brain

Figure 10 -‐ Ventricles in the brain9

Figure 11 -‐ Ventricles as seen on CT10


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Limbic lobe8,11 ⇒ Integrates endocrine function &

autonomic activity with social behaviours

⇒ Major role in converting short-‐term memories to long-‐term & learning

AMYGDALA: emotion (reflexive, eg. fear, anxiety), learning, memory HIPPOCAMPUS: long-‐term memory CINGULATE GYRUS: processing conscious emotional experience FORNIX: connects hippocampus to rest of limbic system Basal ganglia7,12

• Located at base of the forebrain • Lentiform nucleus

(putamen & globus pallidus)

• Corpus striatum (caudate & putamen)

• Amygdala • Claustrum (visual

attention) • Functions:

o Movement o Motivation o Eye movement

Diencephalon7,12

⇒ Lies between the 2 hemispheres, superior to midbrain

⇒ Contains 3rd ventricle ⇒ 4 main components: thalamus, subthalamus, hypothalamus & epithalamus

THALAMUS • Makes up 80% of diencephalon • Relays information from subcortical areas to cerebral cortex

o All sensory systems (except olfactory) have a thalamic nucleus • Processing of cerebral cortical rhythms (ie those seen in EEG)

o Phases of sleep-‐wake cycle o Consciousness, arousal & awareness

• Motor connections from substantia nigra -‐ regulates skeletal muscle movement

y Comprises◦ Amygdala◦ Hippocampus◦ Parahippocampal gyrus◦ Cingulate gyrus◦ Fornix◦ Mammillary bodies ◦ Hypothalamus

y Homeostatic control

y Coordinates instinctive behaviours with higher cortical functioning

y Integrates endocrine function and autonomic activity with social behaviours

y Hippocampus and amygdala are important for converting recent memories to long-term memories and learning

Figure 11 -‐ The limbic system8

Figure 12 -‐ Basal ganglia12


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HYPOTHALAMUS • Lies below thalamus -‐ llinked to pituitary gland, limbic system, visceral & somatic systems • Regulates many metabolic processes & secretes neurohormones which go on to

stimulate/inhibit release of pituitary hormones • Homeostasis: body temp, hunger, thirst, sleep, circadian cycles • Large number of connections with visceral and soamtic systems

Cerebellum7

• Positioned over 4th ventricle • Made up of 2 laterally placed

hemispheres, joined in midline by vermis

• Connects to brainstem via 3 cerebellar peduncles

• Cerebellar nuclei lie deep (gray matter), encased by cerebellar cortex (white matter)

• Receives information from musculoskeletal system, brainstem, thalaus & cerebral cortex

• Functions: o Balance/posture (receives information from vestibular receptors & proprioceptors) o Coordination o Motor learning

Brainstem7,12

⇒ Components are responsible for basic functions of life (cardiac & respiratory centres) ⇒ Site of origin & termination of many cranial nerves

MIDBRAIN

PONS MEDULLA OBLONGATA

Vision Hearing

Motor control Light reflex

Recognition of sound Temperature regulation

Sleep/wake cycles Alertness

Maintenance of awake state Connection between cerebrum

& cerebellum Hearing

Spatial orientation Movement of facial muscles

Continuous with spinal cord Balance

Tongue movement Sensation from head/neck

Cardiac centre Respiratory centre Vomiting centre

Figure 13 -‐ Position of subcortical structures13


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THE NERVOUS SYSTEM 1. Describe the dermatomes and myotomes of the trunk, upper and lower limbs 2. Describe the course and relations of the main nerves of the upper limb and the loss of

cutaneous and motor function that would occur should the median, ulnar, musculocutaneous, radial and axillary nerves to be damaged at various levels within the upper limb

3. Describe the course and relations of the main nerves in the lower limb 4. Describe the loss of function that would result should the main nerves (sciatic, tibial, common

peroneal, obturator, femoral) be damaged at the level of the main joints they cross within the lower limb

5. Describe the basic pattern of dermatome innervation of the trunk and limbs 6. Describe the position and course of the major descending motor pathways within the central

nervous system and determine the motor deficits that would result from lesions affecting different levels of the pathways

7. Describe the position and course of the major ascending pathways within the central nervous system associated with pain, temperature and touch and determine the sensory deficits that would result from lesions affecting the sensory pathways

DERMATOME: area of skin that provides sensory input to a particular set of nerves

` Sensory neurons convey information from skin to CNS

` Dermatomes- areas of skin that provide sensory input to a particular pair of nerves

` Some overlap

` Can be useful for diagnosis

Figure 14 -‐ Dermatomes of the body14


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MYOTOME: a group of muscles innervated by a specific spinal nerve

MOVEMENT MYOTOMES1 UPPER LIMB

Shoulder flexion C5, C6, C7, C8 Shoudler extension C5, C6, C7, C8 Elbow flexion C5, C6 Elbow extension C7, C8 Shoulder abduction C5 Shoulder adduction C6, C7, C8 Medial rotation C6, C7, C8 Lateral rotation C5 Wrist flexion C6, C7 Wrist extension C6, C7 Supination C6 Pronation C7, C8 Finger flexion & extension C7, C8 Finger abduction & adduction T1

MOVEMENT MYOTOMES1 LOWER LIMB

Hip flexion L2, l3 Hip extension L4, L5 Hip adduction L1, L2, L3, L4 Hip abduction L5, S1 Lateral rotation L5, S1 Medial rotation L1, L2, L3 Knee extension L3, L4 (knee jerk reflex) Knee flexion L5, S1 Dorsiflexion L4, L5 Plantarflexion S1, S2 (Achilles reflex) Inversion L4, L5 Eversion L5, S1 Adduction L1, L2, L3, L4 Abduction L5, S1 Lateral rotation L5


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Nerves of the upper limb15

Figure 15 -‐ Nerves of the upper limb16

Figure 15 -‐ The brachial plexus15


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NERVE MOTOR SENSORY DAMAGE Axillary (C5-‐C6)

Teres minor Deltoids

Skin over lower deltoid -‐ “regimental badge area”

Trauma to shoulder # humerus surgical neck

Inability to abduct Radial (C5-‐T1)

Triceps brachii Extensors of forearm

Dorsal surface of lateral 3 ½ digits

Axilla: shoulder dislocation Inability to extend at forearm,

wrist & fingers Wrist drop

Radial groove: # humeral shaft

Triceps brachii weakened but not paralysed

Inability to extend wrist & fingers

Wrist drop Ulnar (C8-‐T1)

Flexor carpi ulnaris Medial half of flexor digitorum

profundus Medial 2 lumbricals Adductor pollicis Interossei of hand Palmaris brevis

Medial 1 ½ fingers Trauma to elbow Inability to grip paper between

fingers (loss of finger abduction + adduction)

Flexion of wrist may still occur Wrist lacerations

Forearm unaffected, loss of finger abduction + adduction Long-‐term -‐ ulnar claw

develops Median (C5/6-‐T1)

Pronator teres Flexor carpi radialis Palmaris longus

Flexor digitorum superficialis Flexor pollicis longus Pronator quadratus Thenar muscles

Lateral 2 lumbricals

Palmar surface of lateral 3 ½ digits

Elbow -‐ Supracondylar # Forearm constantly supinated,

weak flexion Inability to flex thumb

Thenar wasting Wrist lacerations

Thenar muscles paralysed -‐ opposition of thumb affected

Musculocutaneous (C5-‐C7)

Biceps brachii Brachialis

Coracobrachialis

Skin on lateral aspect of forearm

V uncommon -‐ protected within axilla

Weakened (but not absent) shoulder & elbow flexion Supination weakened


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Nerves of the lower limb18

Figure 18 -‐ Nerves of the lower limb17

Figure 16 -‐ Lumbar plexus18

Figure 17 -‐ Sacral plexus18


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NERVE MOTOR SENSORY DAMAGE Sciatic (L4-‐S3)

Muscles of posterior thigh Hamstring portion of adductor magnus

No direct sensory function IM injections/Slipped disc Pain in lower back/hip

Burning, tingling, weakness, numbnss in leg/foot

Hip/buttock pain, worse on sitting (+ signs of distal nervous damage,

depending on site of lesion) Tibial (L4-‐S3)

Popliteus Flexor hallucis longus Flexor digitorum longus

Tibialis posterior Plantaris Soleus

gastrocnemius

Posterolateral & anterolateral side of leg Plantar surface of foot

Direct trauma/entrapment Loss of plantar flexion Loss of toe flexion Weakend inversion

Common peroneal (L4-‐S3)

Muscles of anterior leg, lateral leg & remaining muscles of foot

Lateral leg Dorsasl surface of foot

Fracture of fibular neck Foot drop, inability to evert

Loss of sensation over dorsum & lateral side

Obturator (L2-‐L4)

Obturator externus Pectineus Adductor longus Adductor brevis Adductor magnus Gracilis

Skin over medial thigh Pelvic/abdominal surgery Numbness/paraesthesia over medial

thigh Weakness in adduction (affecting

posture/gait)

Femoral (L2-‐L4)

Iliacus Pectineus Sartorius Quadriceps femoris

Skin on anterior thigh & medial leg

Hip replacement/truma Loss of knee jerk

Pain on hip extension Weakness & wasting of quads

DESCENDING PATHWAYS1, 19

⇒ Originate from cerebral cortex & exit spinal cord via ventral root ⇒ All upper motor neurones ⇒ Control of movement, muscle tone, spinal reflexes, spinal autonomic function & modulation of

sensory transmission to higher centres Pyramidal tracts

⇒ Decussate in medulla Corticobulbular -‐ cranial nerves

• Arises from lateral PMC • Fibres converge and pass through internal capsule to brainstem • Usually bilateral innervation

o Exception: UMN of facial & hypoglossal • Lesions à

o Mild muscle weakness -‐ compensation from contralateral


Safah Sharif 19

Corticospinal (CST) -‐ supplies musculature of body • Control of discrete, skilled movements,

particularly of distal extremities • Fibres descend through internal capsule,

crus cerebri & ventral pons to reach medullary pyramid

• 80% of fibres decussate at pyramids of medulla to form lateral CST

o 10% enter ventral CST o 10% enter lateral CST of same side

• Begin in cerebral cortex, receiving inputs from

o Primary motor cortex (PMC) o Premotor cortex o Supplementary motor area

• Lesions à o Very susceptible -‐ extend almost

whole length of CNS & pass through internal capsule (affected in many CVA)

Extrapyramidal

• Control of movement, posture & muscle tone • Reticulospinal

o Descend from pons & medulla o Involved in control of reflex activities, muscle tone & vital functions

• Vestibulospinal o Transmits to spinal cord, remaining ipsilateral o Control balance & posture by innervating flexors of arms & extensors of legs via LMN

• Lesions à o Dyskinesia/involuntary movements o Eg. degenerative disease, encephalitis, tumours

ASCENDING PATHWAYS19

⇒ Enter spinal cord dorsally, then decussate in CNS so signals are sent to contralateral side Dorsal column

• Fasciculus gracilis & cuneatus carry proprioception & fine touch • Lesions à

o Ataxia, ipsilateral loss of discriminative touch o Eg. B12 deficiency

Spinothalamic tract

• Pain & temperature (lateral SCT) o May ascend several segments before crossing

• Touch & pressure (anterior SCT) o Decussate promptly within 1 segment of origin

• Input relayed to sensory cortex via thalamus • Lesions à

o Impairment on contralateral side

` Control of voluntary, discrete, skilled movements

` Arise in the motor cortex of brain

` Pass through internal capsule

` Cross in medulla (80%)

` Carry out movement in the opposite site on the body

Corticospinal Pathway

PNSCNS

Figure 21 -‐ Corticospinal tract19


Safah Sharif 20

o Dissociated sensory loss (loss of pain/temp, but not touch/pressure)

Dorsal columns

• Fine touch & proprioception • Faciculus gracilis (lower limbs) • Cuneatus (upper limbs) • Starts in muscles, tendons & joint

capsules • Cross in medulla, then relay information

to sensory cortex via thalamus Spinocerebellar tract

• Fibres form dorsal & ventral tracts • Both contain 2nd order neurones,

carrying muscle, joint & tactile input involved in motor control

• Carry information derived from muscle spindles, Golgi tendon organs & tactile receptors to cerebellum for posture control & coordination

• Lesions à o Ipsilateral ataxia

` Sensory for pain, temperature, pressure and crude touch

` Cross at point of entry in spinal cord

` Relayed to the sensory cortex via the thalamus

PNS

CNSFigure 19 -‐ Spinothalamic tract19

` Sensory for proprioception and fine touch

` Cross in the medulla

` Relayed to the sensory cortex via the thalamus

PNS

CNS

Figure 20 -‐ Dorsal column19


Safah Sharif 21

References 1. Module 7 Anatomy Workbook 2. Moore, K. L., Agur, A. M. R., Dalley, A. F. (2015) Essential Clinical Anatomy. 5th ed. Baltimore:

Lippincott Williams & Wilkins 3. Cranial Nerves (2017) Teach Me Anatomy (available on

http://teachmeanatomy.info/head/cranial-‐nerves/) 4. Brooks, L. (2016) Cranial Nerves PBL (9th October 2016) 5. Dansie, P. (2016) Cranial Nerves. Norwich: UEA (Lecture) 6. Vagus Nerves (2014) Health Fixit (available on http://healthfixit.com/vagus-‐nerve/) 7. Dansie, P. (2016) Anatomy of the Brain and Spinal Cord. Norwich: UEA (Lecture) 8. The Ventricles of the Brain (2017) Teach Me Anatomy (available on

http://teachmeanatomy.info/neuro/vessels/ventricles/) 9. Brain Ventricles: Definition & Function (2016) Study.com (available on

http://study.com/academy/lesson/brain-‐ventricles-‐definition-‐function.html) 10. Image:

http://www.lumen.luc.edu/lumen/MedEd/Radio/curriculum/Neurology/Hydrocephalusa.htm 11. Brain Anatomy and Limbic System (2016) Bright Focus Foundation (available on

http://www.brightfocus.org/alzheimers/infographic/brain-‐anatomy-‐and-‐limbic-‐system) 12. Anatomy and Physiology. Boundless (available on

https://www.boundless.com/physiology/textbooks/boundless-‐anatomy-‐and-‐physiology-‐textbook/)

13. Image: http://www.edoctoronline.com/medical-‐atlas.asp?c=4&m=1&p=7&cid=1042&s= 14. Dansie, P. (2016) Peripheral Nervous System. Norwich: UEA (Lecture) 15. Nerves of the Upper Limb (2017) Teach Me Anatomy (available on

http://teachmeanatomy.info/upper-‐limb/nerves/) 16. Image: https://www.slideshare.net/hermizan84/peripheral-‐nerves-‐of-‐upper-‐limb 17. Image:

https://classconnection.s3.amazonaws.com/680/flashcards/1572680/jpg/nerves_of_the_front_leg1359920711805.jpg

18. Nerves of the Lower Limb (2017) Teach Me Anatomy (available on http://teachmeanatomy.info/lower-‐limb/nerves/)

19. Dansie, P. (2016) Neural Pathways. Norwich: UEA (Lecture)

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