NEUROANATOMY

THE BRAIN

4 major parts of the brain:(a) Brain stem(b) Cerebellum(c) Diencephalon (thalamus, hypothalamus,

epithalamus)(d) Cerebrum

(a) Brain stem

Part of the brain between the spinal cord and the diencephalon.3 structures

Medulla oblongataPons

Midbrain

Medulla Oblongata Medulla’s white matter

Ascending (sensory) tracts

Descending (motor) tracts

Pyramids – formed by the large lateral corticospinal tracts that pass from cerebrum to the spinal cord.

90% axons in the left pyramids cross to the right side, vice versa.

To control voluntarymovements of the

limb &trunk.

Decussation of pyramids

Nuclei in medulla

Lateral to the pyramid is olive.

• Inferior olivary nucleus.• Function: receives input from cerebral cortex, red nucleus of midbrain & SC.• Extend axons into cerebellum – provides instruction to cerebellum to make adjustments to the muscles activity as we learn new motor skills

Regulate cardiovascular center

Regulate respiratory center – medullary rhythmicity area: adjust the basic rhythm of breathingControl reflexes for vomitting (vomitting center), swallowing (degluitition center), sneezing, coughing & hiccuping

Nuclei in posterior part of medulla that associate with the dorsal column medial lemniscus (gracile fasciculus & cuneate fasciculus):

Associate with sensations of touch, pressure, vibration & conscious proprioception

Sensory nuclei in the medulla

Gracile nucleus

Cuneate nucleus

Gustatory nucleus (taste)

Cochlear nuclei (hearing)

Vestibular nuclei (balance)

PonsLinks different part of the brainServes as a relay station from medulla to higher

cortical structures of the brain.Respiratory center + medulla rhythmicity area =

control breathing

Midbrain Connects hindbrain & forebrain Cerebral peduncle contains paired bundles of axons :

axons of corticospinal, corticobulbar & corticopontine tracts conducts nerve impulses from motor areas in cerebral cortex to the SC, medulla & pons.

Nerve pathway of the cerebral hemispheres & contains auditory & visual reflex centers

Control responses to sight, eye movement, pupil dilation, body movement & hearing

Posterior part (tectum) Superior colliculiReflex centers for certain visual activities

Inferior colliculiPart of auditory pathway, relaying impulses from the receptors for hearing in the inner ear to the brain

Nuclei of the midbrain

Neurons that extend from here – release dopamine – help control subconcious muscles activities

Rich blood supply & iron-containing pigment in neuronal cell bodies.

Neurons (axons) from cerebellum & cerebral cortex form synapses in red nuclei help control muscular movements

What a physiotherapist should know?

1. There are 4 structures in the ‘midline‘ beginning with M2. There are 4 structures to the ‘side‘ (lateral) beginning with S3. There are 4 cranial nerves in the medulla, 4 in the pons and 4 above the pons(2 in the midbrain)4. The 4 motor nuclei that are in the midline are those that divide equally into 12 except for 1 and 2, that is 3, 4, 6 and 12 (5, 7, 9 and 11 are in the lateral brainstem)

(the Brainstem rule of 4. Doctor Peter Gates)

Medial Structures Deficits

Motor pathway (or corticospinal tract):

contralateral weakness of the arm and leg

Medial Lemniscus contralateral loss of vibration and proprioception in the arm and leg

Medial longitudinal fasciculus

ipsilateral inter-nuclear ophthalmoplegia (failure of adduction of the ipsilateral eye towards the nose and nystagmus in the opposite eye as it looks laterally)

Motor nucleus and nerve

ipsilateral loss of the cranial nerve that is affected (3, 4, 6 or 12)

Lateral structures Deficits

Spinocerebellar pathway

ipsilateral ataxia of the arm and leg

Spinothalamic pathway

contralateral alteration of pain and temperature affecting the arm, leg and rarely the trunk

Sensory nucleus of the 5th cranial nerve

ipsilateral alteration of pain and temperature on the face in the distribution of the 5th cranial nerve (this nucleus is a long vertical structure that extends in the lateral aspect of the pons down into the medulla)

Sympathetic pathway

ipsilateral Homer’s syndrome, that is partial ptosis and a small pupil (miosis)

CN in Medulla Deficits

Glossopharyngeal (CN9)

ipsilateral loss of pharyngeal sensation

Vagus (CN10) ipsilateral palatal weakness

Spinal accessory (CN11)

ipsilateral weakness of the trapezius and stemocleidomastoid muscles

Hypoglossal (CN12)

ipsilateral weakness of the tongue

CN in Pons Deficits

Trigeminal (CN5)

ipsilateral alteration of pain, temperature and light touch on the face back as far as the anterior two-thirds of the scalp and sparing the angle of the jaw.

Abducent (CN6)

ipsilateral weakness of abduction (lateral movement) of the eye (lateral rectus)

Facial (CN7) ipsilateral facial weakness

Auditory (CN8) ipsilateral deafness.The 6th cranial nerve is the motor nerve in the medial pons

CN above Pons Deficits

Oculomotor (CN3)

impaired adduction, supradduction and infradduction of the ipsilateral eye with or without a dilated pupil. The eye is turned out and slightly down

Trochlear (CN4):

eye unable to look down when the eye is looking in towards the nose (superior oblique).The 3rd and 4th cranial nerves are the motor nerves in the midbrain

(b) Cerebellumprimarily contains efferent fibers from the cerebellar nuclei, as well as some afferents from the spinocerebellar tract. 

primarily contains afferents from the pontine nuclei (from motor areas of the cerebral cortex) into cerebellum

primarily contains afferent fibers from the medulla, as well as efferents to the vestibular nuclei

Divisions of the Cerebellum

Functional subdivisions of cerebellum

Cerebrocerebellum• consist of lateral hemisphere& the dentate nuclei.

• its extensive connections with the cerebral cortex, via the pontine nuclei (afferents) and the VL thalamus (efferents).

•Functions:1. Planning & timing

of movement2. Involved in

cognitive function of cerebellum

Functional subdivisions of cerebellum

Vestibulocerebellum• consist of the flocculonodular lobe and its connections with the lateral vestibular nuclei,

• Functions:1. Vestibular reflexes2. Postural

maintenance

Functional subdivisions of cerebellum

Spinocerebellum •Consist of the vermis and the intermediate zones , as well as the fastigial and interposed nuclei.

•it receives major inputs from the spinocerebellar tract.

•Its output projects to rubrospinal, vestibulospinal, and reticulospinal tracts.

•involved in the integration of sensory input with motor commands to produce adaptive motor coordination.

What happened when there is damage to the cerebellum?

1. Decomposition of movement2. Intention tremor3. Dysdiadochokinesia 4. Deficits in motor learning

(c ) Diencephalon (thalamus, epithalamus & hypothalamus)

Extends from the brainstem to the cerebrum & surrounds 3rd ventricle: thalamus, hypothalamus & epithalamus

•Surrounded by cerebral hemisphere.•Contains numerous nuclei involved in wide variety of sensory & motor processing between higher & lower brain.

Thalamus

The intermediate mass (interthalamic adhesion) : a bridge of gray matter

The internal medullary lamina: a vertical Y-shaped sheet of white matter

Functions: to divide right side & left side of thalamus gray matter

Internal capsule: pathway for axons connect the thalamus & cerebral cortex.

Functions of thalamus: Major relay station for most sensory impulses that

reach primary sensory areas of the cerebral cortex from SC & brain stem.

Motor function (transmit information from the cerebellum & basal nuclei to the primary motor area of the cerebral cortex)

Relays nerve impulses between different areas of the cerebrum & plays a role in maintenance of consciousness.

Receives input: the hypothalamusSends output: the limbic systemFunctions: emotions & memory

Receive input: the limbic system& basal nucleiSend output: cerebral cortexFunctions: emotions, learning, memory & cognition

Lateral group nucleiReceives input: the limbic system, superior colliculi & cerebral cortexSends output: the cerebral cortex.

Functions: expressions of emotions

Functions: Help integrate sensory information

Receives input: the basal nucleiSends output: motor areas of cerebral cortexFunctions: plays a role in movement controlReceives input:the cerebellum & the basal nucleiSends output: motor areas of cerebral cortexFunctions: plays a role in movement control

Relays impulses for somatic sensations: touch, pressure, vibartion, itch, tickle, temperature,pain & proprioception from face & body to the cerebral cortex.

Relays impulses for sight from retina to the primary visual area of the cerebral cortex.

Relays auditory impulses for hearing from the ear to the primary auditory area of cerebral cortex

Intralaminar nuclei (within the internal medullary lamina)•Connects with the reticular formation, cerebellum, basal nuclei & wide areas of the cerebral cortex.•Function: - Arousal (activation of the cerebral cortex from the brain stem reticular formation)- Integration of sensory & motor information

Midline nucleus• a thin band adjacent to the 3rd ventricle•Functions: memory & olfaction

Reticular nucleus• lateral aspect of the thalamus•Functions: monitors, filters & integrate activities of other thalamic nuclei.

Body temperature

Water balance/stress

Shivering

GI tract

satiety

Feeding

Body clock

Water balance

Blood pressure

Hypothalamus

Important functions of the hypothalamus:Control of the ANSProduction of hormonesRegulation of emotional & behavioral patternsRegulation of eating & drinkingControl of body temperatureRegulation circadian rhythms& states of

consciouness

Epithalamus

The pineal gland•Part of endocrine system – secretes hormone melatonin•More melatonin liberated during darkness – promote sleepiness•If taken orally – melatonin contribute to the body’s clock setting by inducing sleep & helping the body to adjust jet lag

The Habenular nuclei•Involved in olfaction (emotional responses to odors)

(d) Cerebrum •Primarily of myelinated axons in 3 types of tracts:(a)Association tracts – conduct nerve

impulses between gyri in the hemisphere.(b) Commisural tracts (corpus

callosum, anterior commissure & posterior

commisure) –conduct nerve impulses from gyri one

cerebral hemisphere to corresponding gyri in

otherCerebral hemisphere.(c ) Projection tracts –

conducts nerve impulsesfrom cerebrum to lower part of CNS

(thalamus,brainstem /SC) of from lower parta of

the CNSTo the cerebrum.

• Also known as cerebral cortex.

• Gyri : folds• Fissures: the deepest

grooves• Sulci: the shallower

grooves between folds• Longitudinal Fissue:

prominent fissures that divide brain into cerebral

hemisphere

Basal Nuclei / Basal Ganglia receive input from cerebral cortexProvide output to motor parts of the cortex via the medial & ventral group nuclei of thalamusMajor function: •To help regulate initiation and termination of movement•Globus pallidus: helps regulate muscle tone required for specific body movements•Control subconscious contraction of skeletal muscles•Initiate and terminate cognitive processes (attention, memory, planning & act with limbic system to regulate emotional behaviors

The Limbic System “emotional brain” Functions: Promotes range of

emotions, including pleasure, pain, docility, affection, fear & anger.

Works together with cerebrum for memory functions – damage to the limbic system cause memory impairment

Primary Motor Area•Voluntary contractions of specificBroca’s speech area•Speaking & understanding language•CVA – can still have clear thoughts but unable to form words.Premotor area•Storage of motor patternFrontal eye field area•Scanning movements of the eyesPrefrontal cortex•Concentration, elaboration of thought, judgement, inhibition, personality, emotional traits.•Bilateral damage of the area – rude, inconsiderate, incapable of accepting advice, moody, inattentive, less creative.

The primary auditory area• auditory perception & receives information for soundPrimary Olfactory area•Receives impulse for smell & olfactory perceptionFacial recognition area• Stores information about faces &

allow to recognize people by their faces

Wernickes’s area• Translate words into thought• CVA-able to speak but cannot

arrange words in coherent fashion.

Primary Visual Area•Receives visual information & visual perception

Visual Association Area•Allow to recognize & evaluating what is seen

Primary somatosensory area• receives nerve impulses for touch, pressure, vibration, itch, tickle, temperature, pain, proprioception.

Primary gustatory area•Gustatory perception & taste discrimination

Somatosensory association• determine exact shape & texture of an object by feeling it•To determine the orientation of the object•To sense the relationship of one body part to another•Enable to compare current sensation with previous experiences