Functional anatomy of the brain/spinal cord

What are the 3 basic functions of the nervous system?

Sensation → integration → reaction

CNS vs PNS

CNS = brain and spinal cord;

PNS = cranial/spinal nerves and ganglia

PNS functions in the body? (Somatic vs Autonomic)

Somatic = Controls sensory /muscle voluntary muscle movement

Autonomic = controls sensory/ muscle unvoluntary muscle movement

What is the cerebrum?

The largest region of the brain, derived from the telencephalon

What is a sulcus and what are the main sulcus?

they are shallow grooves between gyri and the main ones are

- Central Sulcus(Rolando fissure)

- Lateral Sulcus(Sylvian fissure)

- Parietoccipital sulcus

Gray matter

Contains neuronal cell bodies, dendrites, and synapses

• Process information

White matter

Contains bundles of myelinated axons organized into tracts (60 percentof brain →myelin bundles → tracts)

What are the common white matter tracts and what do they connect?

Commisural fibers: Interconnect homologous between 2 hemispheres.

Projection fibers: Connect the cortex to the brain stem and spinal cord

Association fibers: Connect the cortical areas within different cortical areas

What does the cerebral cortex contain and its significance?

~90% of the cortex; contains 6 neuronal layers (1-6) and most gray matter

10% of the cortex = allocortex; includes olfactory cortex and hippocampus

BA 3, 1, 2

Primary somatosensory cortex

BA 4,6,8

Primary motor cortex

BA 17,18,19

Primary visual cortex

BA 41–42

Primary auditory cortex

BA 44–45

Broca's area- motor speech

What are the 4 major cerebral lobes?

Frontal, parietal, temporal, and occipital

Frontal lobe functions

Voluntary motor control, executive functions, and language production

Motor homunculus

Face represented laterally; leg represented medially

Premotor cortex

BA 6; sensory-guided movement and control of proximal/trunk muscles

Supplementary motor area

Plans movement sequences and coordinates bilateral movements

Frontal eye fields

BA 8; control saccadic eye movements and visual attention

Prefrontal cortex executive command center

Dorsolateral = working memory, motor planning

Orbitofrontal = impulse control, emotional decision making

Medial = Micturition center

Ventrolateral = Motor inhibition, spatial attention

Broca's aphasia

Non-fluent speech with relatively intact comprehension affecting broadman’s areas 44 and 45. Recieves input from Wernicks area via arcuate fasciculus.

Arcuate fasciculus

Connects Broca's and Wernicke's areas

Parietal lobe locations/ anatomy

Posterior to frontal (central sulcus)

Anterior to occipital (parietal-occipital sulcus)

Dorsal to temporal (lateral sulcus)

Postcentral gyrus

Contains the primary somatosensory cortex

Sensory homunculus

Face represented laterally; leg represented medially

What determines cortical representation of a body part?

Sensory receptor density rather than body size

Posterior parietal cortex

Visuospatial perception, spatial attention, and multisensory integration. BA 5 and 7.

Angular gyrus

Language, reading, mathematics, and theory of mind

left angular gyrus → Gerstman’s syndrome

Supramarginal gyrus

Phonological processing; Wernicke area complex (BA40)

Somatosensory cortex

postcentral gyrus, contralateral touch, proprioception, pain, temperature via thalamus

Posterior parietal cortex

Visuospatial integration, dorsal stream, progects to frontal motor mass

-Right parietal lesion→ hemispatial neglect

Temporal lobe: Location and Anatomy

Inferior to the lateral sulcus (sylvian fissure); Anterior to occipital lobe

Contains:

• Limbic system region

• Wernicke’s Area

• auditory complex

• Sup/mid/inf temporal gyrus

where is the Auditory cortex?

Located in sup. temporal gyrus (Heschl’s gyrus) → like tonotrophic map

Wernicke's area

BA 22(posterior); speech comprehension

• Often described as Inferior frontal gyrus

Wernicke's aphasia

Fluent but nonsensical speech with impaired comprehension

Hippocampus

Medial temporal structure involved in long-term declarative and spatial memory

Damage → retrograde amnesia (unable to form new memories)

Amygdala

Important for fear, emotion, motivation, and emotional memory

damage → impairment fear conditioning

Limbic lobe

Important for emotion, memory, motivation, attention, and autonomic control

Olfactory pathway

Olfactory nerve → olfactory bulb → piriform cortex → medial dorsal thalamus

What is unique about olfaction?

The initial olfactory pathway bypasses the thalamus

Insula

Deep within the lateral sulcus; involved in taste, interoception, autonomic integration, and affective pain

Occipital lobe

Main lobe for visual processing (smallest lobe)

Primary visual cortex

V1; BA 17; located in the calcarine sulcus (left visual field from right, right to left)

Ventral visual stream

"What" pathway; object/face recognition and identity (V1,2,4, inf temporal cortex)

Dorsal visual stream (Where/ How pathway)

V1,2,V5/MT, posterior parietal cortex; Motion, spatial location, depth perception

Meyers loop meaning and lesion relevance

visual → opposite hemifield (Upper field → lower field)

Lesion can damage Meyers loop → ‘pie in the sky” superior quadrantanopia

Where does the adult spinal cord terminate?

Approximately at L1–L2

What is the conus medullaris?

The tapered inferior end of the spinal cord

-spinal tap is at L3/L4 below conus medularis

How many spinal cord segments/ nerves are there?

31: 8 cervical (upper limb via brachial plexus), 12 thoracic, 5 lumbar (lower limb via lumbosacral plexus), 5 sacral, 1 coccygeal

(nerves are same but in pairs so 31 pairs)

Dermatome

Area of skin supplied by a spinal nerve sensory distribution

Myotome

Muscle group controlled by motor fibers from a spinal nerve

Spinal chord protective shield

-Dura Mater - tough outer layer

-Arachnoid mater - middle layer w/ CSF

Pia Mater - close attached to SC

Spinal cord gray matter

Internal and butterfly-shaped; contains neuronal cell bodies

Spinal cord white matter

External; contains myelinated axons

What are the 3 spinal cord funiculi?

Anterior (voluntary movement)

lateral (Sensory/motor)

Posterior (fine touch, proprioception)

What is the subarachnoid space?

The space containing CSF around the spinal cord

What are the 4 functional zones of spinal cord gray matter?

Somatic sensory, visceral sensory, visceral motor, and somatic motor

Lateral horn

Contains autonomic neurons; emphasized at T1–L2 and S2–S4 T1-12

Rexed lamina I (marginal zone)

Relays pain and temperature

Substantia gelatinosa (laminae II–IV)

Processes pain, temperature, and light touch

Dorsal nucleus of Clarke

Unconscious proprioception; C8–L3

Dorsal column

Fine touch and proprioception

Pyramidal/corticospinal tract

Voluntary motor control

Spinocerebellar tract

Proprioceptive information to the cerebellum

Anterior spinal artery

Provides major blood supply to the anterior spinal cord

Internal vertebral venous plexus

Located in the epidural space and communicates with cerebral dural sinuses

Anterior cord syndrome

Associated with anterior spinal artery occlusion

Central cord syndrome

Associated with hyperextension injury and syringomyelia

Brown-Séquard syndrome

Spinal cord hemisection syndrome