BB2

Year MBBS

What is the ventricular system responsible for?

Production, transport and removal of CSF

Where is the thalamus and what is its function?

Lies on either side of the 3rd ventricle

Receives input from all areas of the nervous system (acts as a gateway)

What happens to the proportion of grey: white matter as you go further down the spinal cord?

More white and less grey matter

What is Brown-Sequard syndrome?

A hemisection lesion of the cord resulting in:

• DCML loss on SAME side of injury

• Spinothalamic on OPPOSITE SIDE

How is the DCML tested?

1. vibration sensation via tuning fork

2. position sense (Romberg's test)

3. discriminative sensation

What is the difference between slow and fast pain?

Slow- poorly localised + doesn't trigger reflexes (C fibres)

Fast-connected to myelinated A delta fibres + trigger protective reflexes

Outline 3 main differences between UMN and LMN

UMN: SPASTIC

• found in CNS

• afferent fibres

• large cell bodies

LMN: FLACCID

• in ventral horn

• efferent fibres

• small cell bodies

What are the three main functions of the brainstem?

Conduit (spinal tracts pass through)

Cranial nerve functions

Integrative centres e.g. nucleus ambiguus + reticular formation

Describe the pupillary light reflex

Pupils of both eyes decrease in diameter when either is exposed to light

In via CN II, out via CN III

Describe the vestibulo-ocular reflex

Direction of gaze stays on object to compensate for head movement

In via CN VIII, out via CN III + VI

Describe the blink reflex

Protection of the eye

In via CN V, out via CN VII

What is bitemporal hemianopia?

TEMPLES ONLY
Lesion of the optic chiasm

What is homonymous hemianopia?

SAME SIDE

Lesion of the optic tract

Define glaucoma

Increased intraocular pressure leading to damage of the optic nerve

2 subtypes- open angle (chronic) and closed angle (acute)

What is the canal of Schlemm?

Drains aqueous humour to reduce intraocular pressure

Damage could result in glaucoma

Outline 4 functions of a glial scar

Engulfs debris
Seals lesion site
Repairs blood- spinal cord barrier
Expresses chemicals that inhibit axon growth

What are the 2 main barriers to CNS repair?

Hostile environment

Poor regenerative response compared to PNS
+ very slow clean up due to reduced macrophages

What are the 3 ways of preventing neurodegeneration after trauma?

1. neuroprotection by containing effects of early trauma, inflammation + scar formation

2. promotion of axonal regeneration

3. guiding axonal regrowth via scaffolds + grafts

What are the 2 main nuclei found in the hypothalamus?

Paraventricular nucleus

Supraoptic nucleus

What is the HPA axis?

Hypothalamic-pituitary-adrenal axis which is a negative and positive feedback system that regulates release of hormones

What is the hypophyseal portal system?

System of blood vessels in the brain that connects the hypothalamus with the anterior pituitary

What happens when Broca's equivalent is damaged?

Results in aprosodia- monotonous, normal pauses and tone/ inflection are absent

What is the function of the arcuate nucleus?

Fibre bundle that connects Broca's and Wernicke's areas

What is the mechanism of an excitatory postsynaptic potential (EPSP)?

1. ACh binds to nAChR and opens Na+ channel

2. allows Na+ into neuron :. causing depolarisation

What is the mechanism of an inhibitory postsynaptic potential (IPSP)?

1. GABA binds to GABAa receptor + allows influx of Cl-

2. resting potential becomes more negative

3. membrane is more leaky to current

Outline 5 functions of the reticular formation

1. somatic motor control- reticulospinal tracts responsible for muscle tone, balance + posture

2. cardiovascular and respiratory control- vasomotor and apneustic centres in pons

3. pain modulation

4. sleep and consciousness

5. habituation- ignores repetitive, meaningless stimuli (esp during sleep) but still sensitive to others

What is the lateral reticular formation responsible for?

Swallowing, coughing, sneezing, vasomotor and vomiting

What are the basal ganglia?

Masses of grey matter located deep within the cerebral hemisphere e.g. caudate nucleus, substantia nigra and raphe nuclei

Describe the main features of the ascending tracts

Spinothalamic: crude touch, pain, temp. Decussates ASAP, primary somatosensory

DCML: vibration, proprioception, discriminative touch. Decussates medulla, primary somatosensory

Spinocerebellar: subconscious proprioception. NO decussation, cerebellum

Describe the main features of the corticospinal tract

Transmits motor signals from cortex to spinal cord

Decussates in medulla

Describe the essential differences between afferent and efferent nerves

AFFERENT: sensory neurons that carry nerve impulses from sensory stimuli to CNS

EFFERENT: motor neurons that carry nerve impulses to muscles

Name 2 proprioceptors

Muscle spindles (length) and golgi tendon organs (tension)

Compare the sensory receptive fields in different parts of the body

Fingers: shorter :. more neurons supplying small area of skin. HIGHER RECEPTOR DENSITY

Back: one neuron covers a lot more area :. touch is far less localised. LOWER RECEPTOR DENSITY

Explain what a two-point discrimination test is and how to perform it correctly

Measures tactile spatial acuity

Callipers used to assess ability of individual to determine between 2 points

Minimum distance at which subject can make distinction\= threshold

Higher density of receptors in skin + smaller receptive field\= finer discrimination for mechanoreception (i.e. finger pads)

List the changes that occurs after nerve injury

1. distal part begins to degenerate as its no longer connected to the cell body

2. schwann cells unwrap themselves+ divide to form continuous line of cells lining distal endoneurial sheaths

3. proximal cut ends of nerve fibre form growth cones + grow back down inside sheath with help of cell adhesion molecules

4. actin contracts to pull cone along towards denervated region

5. macrophages + microglia engulf debris and injury site becomes walled off by glial scar

Define what is meant by glial scar

Reactive cellular process following injury to the CNS

Acts as a physical and chemical barrier

Roles:

• engulf debris

• seals lesion site

• repairs blood-spinal cord barrier

• expresses chemicals that inhibit axon growth

What is Wallerian degeneration?

Active process of retrograde degeneration of distal end of axon following nerve lesion

Occurs 7-21 days after injury

Outline the features of UMN lesions

Present deep tendon reflexes (hyperreflexia)

Babinski positive (dorsiflexion + fanning of foot when scraped)

Spastic paralysis

Outline the features of LMN lesions

Muscle atrophy

Absent deep tendon reflexes (hyporeflexia)

Fasciculations

No Babinski

Flaccid paralysis

Describe the function of muscle spindles

Located within muscle fibre

Senses muscle stretch/ lengthening

Sends nerve impulse to spinal cord which immediately synapses with LMN to act on muscle

Results in muscle shortening aka contraction

Also involved in reciprocal inhibition by inhibiting (relaxing) antagonist muscle

Describe the function of Golgi Tendon Organs

Located in tendon

Senses tension as tendon doesn't change in length

Inhibits further muscle action to prevent damage to muscle and tendon

Known as autogenic inhibition

List the 5 components of the reflex arc

1. receptors

2. afferent neuron

3. integrating centre e.g. spinal cord

4. efferent neuron

5. effector

Describe the patellar tendon reflex

1. activation of receptor when GTO is stretched

2. action potentials fired by 1a afferents which synapse with motorneurones in spinal cord (excitatory and inhibitory)

3. hamstrings inhibited via inhibitory interneuron + quadriceps muscle contracts

MONOSYNAPTIC

What are polysynaptic reflexes?

When afferents and efferents are connected via interneurons

e.g. withdrawal reflex is intended to protect the body from damaging stimuli.
Don't only send signals to agonist muscle but also antagonistic muscle and associated centres in brain to process what occurred

Outline the clinical testing of the extraocular muscles

SR + IR: abduct eye then look up/down

SO + IO: adduct eye then look up/down

MR + LR: unopposed abduction or abduction of eye

Which foramina do the CNs pass through?

I: cribriform plate

II: optic canal

III: superior orbital fissure

IV: superior orbital fissure

V1: superior orbital fissure

V2: foramen rotundum

V3: foramen ovale

VI: superior orbital fissure

VII: internal acoustic meatus

VIII: internal acoustic meatus

IX: jugular foramen

X: jugular foramen

XI: jugular foramen

XII: hypoglossal canal

Explain the role of the different components of the spinothalamic tracts in sensation and pain

Anterior- carries sensory modalities of crude touch and pressure

Lateral- carries sensory modalities of pain and temperature

Briefly describe the clinical manifestations of lesions of the spinal cord

Small central: *centrally crossing fibres of spinothalamic tract*, loss of pain + temperature sensitivity

Most common in CERVICAL cord

Large central: loss of pain + temp sensitivity, AT LEVEL OF LESION-\> LMN damage, BELOW LEVEL-\> UMN damage

Hemisection (BS syndrome): ipsilateral DCML below lesion, contralateral spinothalamic

Complete transection: loss of sensory and motor below level

Explain the consequences of raised pressure in the posterior cranial fossa

Fossa protects- brainstem, cranial nerves, basilar and vertebral arteries and ventricular system

Symptoms: headache, blurred vision, hypertension, bradycardia and irregular breathing

Long term high pressure may result in brain injury, seizure, coma, stroke or death

List the symptoms associated with damage to CNs 1-4

Olfactory: loss of sense of smell or extreme awareness of bad odour

Optic: optic atrophy, visual field disorders, blurred vision etc

Oculomotor: diplopia, down and out eyes

Trochlear: vertical diplopia

List the symptoms associated with damage to CNs 5-8

Trigeminal: pain in face, paralysis of mastication muscles

Abducens: unopposed action of medial rectus :. looking inwards

Facial: Bell's palsy, loss of taste, face paralysis

Vestibulocochlear: hearing impairment, loss of balance

List the symptoms associated with damage to CNs 9-12

Glossopharyngeal: tongue, throat, tonsil and ear pain

Vagus: swallowing paralysis, vocal cord weakness, hoarseness, pain. Uvula deviates AWAY

Accessory: flatness of neck + inability to rotate head and raise shoulders

Hypoglossal: lingual paralysis deviates TOWARDS lesion

Describe the 3 types of nerve damage

Neuropraxia- endoneurium and axon intact, mild demyelination :. mild conduction block/sensory/ motor loss *complete recovery*

Axonotmesis- endoneurium intact, damage to axon + mild demyelination :. conduction block *complete recovery*

Neurotmesis- endoneurium + axon damage + severe demyelination :. severe conduction block *poor recovery + bad prognosis*

Define the term neuromodulator and give examples

Neurons used one or more chemicals to regulate diverse populations of neurons

Triggers GPCR

Compare the functions of the superior laryngeal nerve and recurrent laryngeal nerve

Superior:

• internal branch-> sensation above glottis

• external branch-> supplies cricothyroid muscle which is responsible for pitch pathology

Recurrent: sensation below glottis, motor to all other intrinsic muscles of larynx. Responsible for phonation :. pathology-> hoarseness + stridor

Describe the vasculature of the neck

Superficial temporal
Ascending pharyngeal
Lingual
Facial
Occipital
Posterior auricular
Maxillary
Superior thyroid

Some Anatomists Like Freaking Out Poor Medical Students

What does it mean when the vocal cords increase in length?

Higher pitch

Controlled by cricothyroid + supplied by external (superior) laryngeal nerve

Through which bone does the facial nerve travel through before exiting the skull via the stylomastoid foramen?

Petrous temporal bone

What artery supplies the anteromedial portion of the cerebrum?

Anterior cerebral artery

How is ghrelin released in the stomach?

At the fundus of the stomach by the enteroendocrine cells

What are the differences between Wernicke's aphasia, Broca's aphasia and conduction aphasia?

Wernicke's: can speak fluently but in a meaningless way

Broca's: can understand speech but cannot articulate properly- often having halted speech

Conduction: impaired ability to read out loud and repeat back speech

Which sensory nerve ending is responsible for the continued dull pain and what spinal tract does this sensory information pass through?

C nociceptor fibres

Spinothalamic

Which structure passes through foramen rotundum?

CN V2

Through what mechanism of action do beta-adrenergic receptor antagonists help with in the treatment of glaucoma?

Decrease aqueous humour production

How does ghrelin affect neurons that release NPY (Neuropeptide Y), AgRP(Agouti-related peptide), POMC (proopiomelanocortin) and CART (Cocaine and Amphetamine related transcript neurons)?

ACTIVATES: NPY and AgRP -releasing neurons

INHIBITS: POMC and CART

:. inducing hunger

State the main regions of the anterior triangles of the neck

Main areas- submandibular, submental, carotid and muscular

Separated from posterior triangle by SCM

State the boundaries and contents of the carotid triangle

Boundaries:

• superior= posterior belly of digastric muscle

• lateral= medial border of SCM

• inferior= superior belly of omohyoid muscle

Contents: common carotid artery, internal jugular vein, hypoglossal and vagus nerves

List all the suprahyoid and infrahyoid muscles

Supra: superheroes do much good

• stylohyoid

• digastric

• mylohyoid

• geniohyoid

Infra: otis sits tests slowly

• omohyoid

• sternohyoid

• thyrohyoid

• sternothyroid

State the main regions of the posterior triangles of the neck and their boundaries

Occipital and supraclavicular

Posterior- trapezius
Anterior- SCM
Inferior- clavicle

Describe Horner's syndrome

Damage to cervical sympathetic trunk

Results in:

• contraction of pupils (miosis)

• drooping of superior eyelid (paralysis of LPS-> ptosis)

• sinking of eye

• vasodilation + absence of sweating (anhidrosis)

Define the term 'grandmother cell'

A neuron that only responds to a highly specific stimulus :. fires significantly more when presented with an image of person grandmother or similar

Also called Jennifer Aniston neuron

Explain the functions of the posterior parietal cortex

Receives input from a collection of sensory areas + other regions of the brain

Role in spatial cognition and motor control of eyes + extremities

Describe the functions of the inferior temporal cortex

Visual processing and visual object recognition

Describe the functions of the dorsolateral prefrontal cortex

Executive function, response selection and working memory

Partial optic nerve lesion

Ipsilateral scotoma

Optic chiasm lesion

Bitemporal hemianopia

Optic tract lesion

Homonymous hemianopia

Complete optic nerve lesion

Blindness in that eye

Describe the accommodation reflex

Response to focusing on near object, then looking at distant object

3 main components:

• thickening of lens (ciliary muscles contract)

• convergence (bent angle of eyes)

• pupil constriction

Define photo-transduction

Process through which photons are converted into electrical signals

Describe the main difference between rods and cones

Rods: scotopic vision-\> dim/dark light

Cones: bright light

Describe cataracts

Lens become opaque/cloudy

• develops slowly

• reduces levels of antioxidants in aqueous humour

• risk factors: diabetes, hypertension, exposure to excess UV light/microwaves

What are the 3 main neurons in the path from photoreceptor to optic nerve?

1. photoreceptors

2. bipolar cells

3. ganglion cells

Describe the 4 parts of the internal carotid artery

Cervical
Petrous (in carotid canal)
Cavernous (sinus)
Cerebral

What does the anterior cerebral artery supply?

Medial frontal and parietal lobes

What does the middle cerebral artery supply?

Lateral surface of cerebral hemispheres

Except superior frontal + parietal lobes and inferior temporal lobe

Name the branches of the vertebral artery

Anterior spinal a.
Posterior inferior cerebellar a.
Basilar a. (brainstem + cerebellum)
Anterior inferior cerebellar a.
Superior cerebellar a.
Posterior cerebral a.

Outline the primary function of the circle of Willis

Provides redundancy :. permits circulation even if a part of the circle is occluded via communicating a.

Describe the hypothalamo-hypophyseal tract

Collection of nerves, endocrine tissue and blood vessels in the hypothalamus and pituitary gland

Secrete:

• hormones that directly produce responses

• hormones that regulate synthesis + secretion of hormones of other glands

Describe 6 hypothalamic releasing hormones

Corticotrophin RH-\> adrenocorticotrophic H

GnRH-\> LH + FSH

Thyrotropin RH-\> thyroid stimulating H

Growth hormone RH-\> GH

Growth hormone inhibiting hormones

Prolactin inhibiting factor

Describe the hypophyseal portal system

Capillary bed in infundibulum connecting hypothalamus to anterior pituitary

Allows hypothalamic hormones to be transported to anterior pituitary without entering systemic circulation first

Describe the afferents of the hypothalamus

NST- blood pressure, gut distension

Reticular formation- body temperature

Retina- sleep/wake cycle

Limbic + olfactory system- smell, emotion

Explain the structure of the BBB and its functional significance

Astrocytes
Pericytes
Endothelial cell
Basement membrane
Tight junctions

Selectively permeable membrane that protects brain from toxins and infections

Describe the movement of CSF

1. formed in choroid plexus of lateral ventricles

2. travels down interventricular foramen to 3rd ventricle

3. down via cerebral aqueduct to 4th ventricle

4. through median aperture to back of cerebellum + down outside of spinal cord

5. absorbed by arachnoid granulations in superior sagittal sinus + joins venous blood

What are cisterns of the brain?

Areas where the subarachnoid space expands due to the curvature of the brain surface

Describe the main types of brain haemorrhage

1. epidural: between dura mater + skull (contained dome shape)

2. subdural: between dura + arachnoid (contained but spread out)

3. subarachnoid: in subarachnoid space (spread)

4. intracerebral: in brain tissue

What are the main afferents and efferents of the reticular formation?

Afferents: sensory pathways (optic, auditory, etc), cortex, thalamus, cerebellum

Efferents: substantia nigra, cerebellum, tectum, cortex, thalamus, hypothalamus

Describe the main functions of the auditory system

Hearing

• distinguish between different sounds

• localise where sound is coming from

Language

• production

• comprehension

Outline the functions of the outer ear

Protection

Localisation

Amplification (due to diameter of pinna)

Mode of operation: air vibration

Outline the functions of the middle ear

Impedance matching- generates vibration in cochlea fluid to reflect sound

Pressure equalisation (eustachian tube)

Inner ear stimulation

Mode of operation: mechanical vibration