Functional Anatomy & Physiology

Dr. Ra’ed Ahmed

MBChB, FIBMS

Neurologist March 31 - 2015

Lec. 1

09.00 AM

1

Functions of the Nervous System

1. Sensory input – gathering information

To monitor changes occurring inside and outside the body (changes = stimuli).

2. Integration –

to process and interpret sensory input and decide if action is needed.

3. Motor output

A response to integrated stimuli.

The response activates muscles or glands.2

Structural Classification of the Nervous System

Central nervous system (CNS)

Brain

Spinal cord

Peripheral nervous system (PNS)

Nerve outside the brain and spinal cord

3

Organization of the Nervous System

4

Nervous Tissue: Support Cells (Neuroglia or Glia) of CNS

Astrocytes (largest of neuroglia)

Abundant, star-shaped cells

Brace neurons

Form barrier between capillaries and neurons

Control the chemical environment of the brain (CNS)

5

Nervous Tissue: Support Cells

Microglia (CNS)

Spider-like phagocytes

Dispose of debris

Ependymal cells (CNS)

Line cavities of the brain and spinal cord

Circulate cerebrospinal fluid

6

Nervous Tissue: Support Cells

Oligodendrocytes

(CNS)

Produce myelin

sheath around

nerve fibers in the

central nervous

system

7

Support Cells of the PNS

Satellite cells

Protect neuron cell bodies

Schwann cells

Form myelin sheath in the peripheral nervous system

Figure 7.3e

8

Neuron Anatomy

Slide 7.9b

Cell body : nucleus large nucleolus

Dendrites – conduct impulses toward the cell body

Axons – conduct impulses away from the cell body

Figure 7.4a

9

10

Central Nervous System (CNS)

CNS develops from the embryonic neural tube

The neural tube becomes the

brain and spinal cord

The opening of the neural tube

becomes the ventricles

Four chambers within the brain

Filled with cerebrospinal fluid 11

Brain Part of CNS that lies within the cranial

vault, the encephalon.

Its hemispheric surface is convoluted and has gyri and sulci

Weighs 350 g in the newborn and 1400 g in the adult.

The male brain is on average slightly heavier than the female brain

12

Regions of the Brain

Cerebral hemispheres

Diencephalon

Brain stem

Cerebellum

13

Lobes of the Brain

14

Frontal lobes:

• Reasoning,abstraction,concentration

• Control of voluntary eye

movements.

• Motor control of speech in the

dominant hemisphere.

• Motor Cortex

• Urinary continence.

• Emotion and personality

Parietal lobes:

• Sensory cortex – define size,

weight, texture and consistency

(contralateral).

• Sensation is localised, and

modalities of touch, pressure and

position are identified.

• Awareness of the parts of your body.

• Dominant is involved in ideomotor

praxis

• Non-dominant – visuospatial

information

Temporal lobes:

• Primary auditory receptive areas.

handle visual perception and olfaction.

• Learning and memory, emotional

affect.

• Dominant temporal lobe influences

comprehension of speech.

• Nondominant temporal lobe

mediates prosody and spatial

information

Occipital lobes:

• Primary visual cortex.

• Visual association areas.

• Visual perception.

• Some visual reflexes (i.e. visual

fixation).

• Involuntary smooth eye movements

Brodmann’s areas : mapping the cortical areas of the brain.

19

Motor Homunculus

20

Sensory Homunculus

21

Layers of the CerebrumGray matter

Outer layer

Composed mostly of neuron cell bodies

White matter

Fiber tracts inside the gray matter

Figure 7.13a

22

Basal Ganglia large masses of gray matter deep within

the cerebral hemispheres.

Include the caudate, putamen, and globus pallidus that lie lateral to the thalamus.

Functionally, substantia nigra (SN) and the subthalamic nucleus.

Motor control includes the preparation for and execution of cortically initiated movement

23

24

Diencephalon

Sits on top of the brain stem

Enclosed by the cerebral hemispheres

Made of four parts

Thalamus

Hypothalamus

Epithalamus (roof of the third ventricle Houses the pineal body, choroid plexus)

Subthalamus25

Diencephalon

Figure 7.15

26

Thalamus

Surrounds the third ventricle.

The relay station for sensory impulses.

Transfers impulses to the correct part of the cortex for localization and interpretation.

27

Hypothalamus

Under the thalamus.

Important autonomic nervous system center

Helps to regulate body temperature

Controls water balance

Regulates metabolism, appetite control.

An important part of the limbic system (emotions)

28

Brain Stem

It is a small, narrow region connecting the spinal cord with the rest of the brain

Parts of the brain stem

Midbrain

Pons

Medulla oblongata

29

Brainstem

30

Midbrain

located between the diencephalon and the pons.

Mostly composed of tracts of nerve fibers

Reflex centers for vision and hearing

Cerebral aquaduct – 3rd-4th ventricles

31

Pons

pons means “bridge” in Latin

The bulging center part of the brainstem

Mostly composed of fiber tracts

Includes nuclei involved in the control of breathing

32

Medulla Oblongata

The lowest part of the brain stem

Merges into the spinal cord

Includes important fiber tracts

Contains important control centers

Heart rate control

Blood pressure regulation

Breathing

Swallowing

Vomiting 33

34

Cranial nerves on the anterior surface of the

brain.

Cerebellum or "small brain"

Located in the posterior cranial fossa

Attached to the brainstem by three cerebellar peduncles

Forms the roof of the fourth ventricle

Anatomically divided into the two hemispheres, the midline vermis and the flocculonodulus ,consists of folia and fissures on its surface

Provides involuntary coordination of body movements

35

36

Protection of the Central Nervous System

Scalp and skin

Skull and vertebral column

Meninges

CSF

BBB

37

SKULL

22 bones in total, 8 make up the cranium, other 14 facial bones.

Cranium is that part of the

skull that encloses the brain

3 components within

the cranium have a balance

(80% brain ,

10% blood ,10% CSF).

38

Meninges

Dura mater " hard mother"

Double-layered external covering

Periosteum – attached to surface of the skull

Meningeal layer – outer covering of the brain

Folds inward in several areas (falxcerebri, tentorium cerebelli & falxcerebelli)

39

Meninges

Arachnoid layer " spider"

Middle layer ,extremely thin , nonvascular

Web-like, loosely encloses the brain

Pia mater:

Inner most, delicate highly vascular

Intimately adhere to the brain substance

Spaces of the meninges: extradural, subdural and subarachnoid.

40

Cerebrospinal Fluid CSF

Similar to blood plasma composition

Formed by the choroid plexus

Reabsorbed into the venous blood flow via the arachnoid villi

Produces at a rate (~ 500mL/day) and total volume (~ 150mL)

Buoyancy , Protection ,Transport of nutrients, Removal of waste products

41

Ventricles and Location of the Cerebrospinal Fluid

Figure 7.17b42

43

Spinal Cord Continuous with the

medulla oblongata at the spinomedullary junction terminates caudally as conus medullaris.

Ends at the level of lower border of L1

Enlargements occur in the cervical and lumbar regions

44

Spinal Cord cont.

lies within subarachnoid space and covered by three meningeal coats (pia , arachnoid and duramater).

Averges, in length, 45 cm in males and 42 cm in females

Weighs about 30 g , comprising 2% of the adult brain weight

The spinal cord comprises

31 segments defined by

31 pairs of spinal nerves 45

PNS : Spinal Nerves

Figure 7.22a 46

APPROACH TO THE PATIENT WITH NEUROLOGIC DISEASE

Where is the lesion?

What is the lesion?

Meridians of Longitude= motor, sensory

pathways (location, function, decussation)

–Corticospinal

–Spinothalamic

–Dorsal column – Medial Lemniscus

Parallels of Latitude( Cortex---muscle)

What are the most important regions for anatomic localization?

Cortical Brain

Subcortical Brain

Brainstem

Cerebellum

Spinal Cord

Root

Peripheral Nerve

Neuromuscular Junction

Muscle

How are symptoms localized to these neuroanatomic regions?

Neurologic Examination:

1- Higher Cortical Function

2- Cranial Nerves

3- Cerebellar Function

4- Motor

5- Sensory

6- Deep Tendon Reflexes

7- Pathologic Reflexes

Characteristic of upper motor neurone lesions: UMNL

• No wasting, but from disuse;

• Increased tone “Spasticity” of clasp-knife

type;

• Weakness most evident in anti-gravity

muscles;

• Increased reflexes and clonus;

• Extensor plantar responses.

Characteristics of lower motor neurone lesions: LMNL

• Wasting “pronounced” ;

• Fasciculation;

• Decreased tone (i.e. flaccidity);

• Weakness;

• Decreased or absent reflexes;

• Flexor plantar responses.

Corticospinal Tracts

Pain & Temperature

Position sense

• Ataxia or clumsiness of movement

• Partial compensation by active monitoring of movement by the eyes;

• No weakness.

Patterns of sensory deficit

Clinical features of Cortical Brain lesion

Dominant (usually left) hemisphere is “aphasia”

Nondominant (usually right) hemisphere,

usually causes visual-spatial problems.

Cortical sensory loss such as two-point

discrimination, stereognosis, and

graphesthesia.

Seizures are almost always cortical in origin.

Incomplete hemiparesis, affecting the face and

arm, but not the leg.

The sensory homunculus has a similar

somatotropic arrangement

Clinical features of Subcortical Brain lesion

Higher Cortical Function: normal

Cranial Nerves: visual field cuts

Cerebellar Function: usually normal

Motor: weakness in face=arm=leg ,UMNL

Sensory: sensory abnormalities in

face=arm=leg

Deep Tendon Reflexes: hemi-hyper-reflexia

Pathologic Reflexes: extensor planter reflex

Clinical features of Brainstem disease

The brain stem is essentially the spinal cord with

embedded cranial nerves.

Cranial nerve signs: diplopia, decreased

strength or sensation over the face, dizziness,

deafness, dysarthria, dysphagia

Long tract signs: hemiparesis UMNL or

hemisensory loss

Crossed signs or Bilateral findings

Clinical features of Cerebellar disease

A. Incoordination of muscle activity:

• in the head: nystagmus, dysarthria;

• in the arms: finger–nose ataxia, kinetic

(intention) tremor, difficulty with rapid alternating

movements (dysdiadochokinesia);

• in the legs: heel–knee–shin ataxia, gait ataxia,

falls.

B. Hypotonia ,no Weakness, Sensory: normal

DTRs normal ,Pathologic Reflexes: none

Clinical features of Spinal cord disease

Atriad of symptoms (Sensory level,Spastic

weakness & Bowel and bladder problems)

Distal weakness greater than proximal

weakness (UMN signs below the lesion)

Increased tone (spasticity)

Increased reflexes ,Clonus

Extensor plantar response

Absent superficial reflexes

No significant atrophy or fasciculations

Clinical features of Root diseases (Radiculopathies)

Pain is the hallmark of root disease

Weakness, while asymmetric, may be either

proximal or distal, depending on which roots are

involved

O\ E = LMN findings

Atrophy and fasciculations.

Tone is normal or decreased, and hypo- to a-

reflexia if the root carries a reflex.

Sensory loss occurs in a dermatomal

distribution.

Clinical features of Peripheral neuropathies

Weakness leg, arm : distal predominant

Sensory changes : distal predominant

O\E

Distal, often asymmetric weakness with atrophy,

fasciculations

Muscle tone is often decreased. loss of distal

reflexes, Mute responses to plantar stimulation

Sensory loss

Clinical features of Neuromuscularjunction disease

“Fatigability” “Fluctuation” the hallmark of

NMJ

Proximal symmetric weakness

Weakness is often extremely proximal,

involving muscles of the face, eyes

(ptosis), and jaw.

Muscles are normal in size, without

atrophy or fasciculations, with normal tone

and reflexes.

No sensory loss.

positive response to anticholinesterase.

Clinical features of Muscle disease

Proximal symmetric leg & arm weakness

without sensory loss.

O\E

Muscles : normal in size, without atrophy

no fasciculation;

Tone : normal or reduced;

Reflexes : normal or reduced.

what is the lesion?

Happy Reading !

THANK YOU

76