Brain, Cranial Nerves, and Spinal Cord Lecture

Vocabulary flashcards summarizing major structures, nerves, and concepts from the lecture on Chapters 15–17 (brain, cranial nerves, spinal cord, and spinal nerves).

Diencephalon

Midline portion of the forebrain composed mostly of gray matter; includes thalamus, hypothalamus, and epithalamus.

Thalamus

Makes up ~80 % of the diencephalon; major relay and editing station for incoming sensory signals to the cerebral cortex.

Hypothalamus

Primary autonomic and endocrine control center; regulates body temperature, hunger, thirst, circadian rhythm, emotional responses, and more.

Epithalamus

Posterior segment of the diencephalon that links limbic structures and houses the pineal gland.

Pineal gland

Small epithalamic endocrine gland that resembles a pine cone; secretes the hormone melatonin.

Melatonin

Pineal-gland hormone that helps regulate circadian (sleep–wake) cycles.

Optic chiasma

X-shaped crossover of the optic nerves located inferior to the hypothalamus.

Pituitary gland

Endocrine gland attached to the hypothalamus by the infundibulum; sits in the sella turcica and controls many other glands.

Sella turcica

Depression in the sphenoid bone that cradles the pituitary gland.

Brain stem

Mostly white-matter stalk connecting brain and spinal cord; consists of midbrain, pons, and medulla oblongata.

Midbrain

Superior section of the brain stem; contains visual and auditory reflex centers.

Superior colliculi

Rostral bumps of the tectal plate that mediate visual reflexes (eye tracking).

Inferior colliculi

Caudal bumps of the tectal plate that mediate auditory reflexes (startle to sound).

Pons

‘Bridge’ region of the brain stem; links cerebrum and cerebellum and contains the pontine respiratory center.

Pontine respiratory center

Cluster of neurons in the pons that helps regulate breathing rhythm.

Medulla oblongata

Inferior brain-stem region housing cardiac, vasomotor, and second respiratory centers plus cough/sneeze reflexes.

Decussation of pyramids

Site on the anterior medulla where most motor tracts cross to the opposite side.

Cerebellum

Posterior brain region that integrates motor intentions with body position and head movement to coordinate balance and smooth movements.

Arbor vitae

Tree-like pattern of cerebellar white matter seen in sagittal section; means “tree of life.”

Ipsilateral

On or affecting the same side of the body; describes cerebellar mapping.

Limbic system

Functional system spanning cerebrum and diencephalon; governs emotions and memory.

Cingulate gyrus

Arching cortical fold above the corpus callosum; important in emotional expression and conflict resolution.

Amygdala

Almond-shaped limbic nucleus that stores emotional memories and triggers fear responses.

Reticular formation

Network of brain-stem neurons that extends into the cerebrum; regulates arousal and sensory filtering.

Reticular Activating System (RAS)

Part of the reticular formation that keeps the cerebral cortex alert and screens out repetitive stimuli.

Sensory processing disorder

Condition in which the RAS filters sensory input abnormally, leading to ‘sensory seekers’ or ‘sensory avoiders.’

Cranial nerves

Twelve paired nerves that emerge from the brain (mainly brain stem) to innervate head, neck, and viscera.

Olfactory nerve (I)

Purely sensory cranial nerve carrying smell information from the nasal epithelium.

Optic nerve (II)

Sensory cranial nerve conveying visual input from the retina.

Oculomotor nerve (III)

Motor cranial nerve that controls four extrinsic eye muscles, pupil size, and lens shape.

Trochlear nerve (IV)

Motor nerve to the superior oblique muscle of the eye.

Trigeminal nerve (V)

Mixed cranial nerve with three divisions; main sensory nerve of the face and motor nerve for mastication.

Abducens nerve (VI)

Motor nerve to the lateral rectus eye muscle.

Facial nerve (VII)

Mixed nerve; motor to facial-expression muscles and some salivary glands, sensory for anterior taste buds.

Vestibulocochlear nerve (VIII)

Sensory nerve composed of vestibular (balance) and cochlear (hearing) branches from the inner ear.

Glossopharyngeal nerve (IX)

Mixed nerve; sensory from posterior tongue/throat (taste), motor to a salivary gland and pharyngeal muscle.

Vagus nerve (X)

Longest cranial nerve; mixed, supplying parasympathetic motor fibers and sensory input to thoracic-abdominal viscera.

Accessory nerve (XI)

Motor nerve to sternocleidomastoid and trapezius muscles.

Hypoglossal nerve (XII)

Motor nerve controlling tongue movement.

Spinal cord

Continuation of the medulla running to approximately L1; conducts impulses to/from the brain and mediates reflexes.

Conus medullaris

Cone-shaped tapered end of the spinal cord around L1.

Cauda equina

Bundle of lumbar, sacral, and coccygeal spinal nerves that resemble a horse’s tail below the conus medullaris.

Cervical enlargement

Thickened spinal-cord region that supplies nerves to the upper limbs.

Lumbosacral enlargement

Expanded cord region supplying nerves to the lower limbs.

Central canal

Small channel in the spinal cord that carries cerebrospinal fluid.

Gray commissure

Bridge of gray matter connecting right and left sides of the spinal cord around the central canal.

Posterior horn

Narrow dorsal gray-matter projection reaching the cord surface; contains interneurons receiving sensory input.

Anterior horn

Rounded ventral gray-matter projection containing somatic motor neurons.

Posterior funiculus

Dorsal column of spinal white matter containing ascending sensory tracts.

Ascending tract

Bundle of axons carrying sensory information up the spinal cord toward the brain.

Descending tract

Bundle of axons carrying motor commands from the brain down the spinal cord.

Posterior (dorsal) root

Sensory root of a spinal nerve; contains afferent fibers entering the cord.

Anterior (ventral) root

Motor root of a spinal nerve; contains efferent fibers exiting the cord.

Dorsal root ganglion

Swelling on the posterior root containing cell bodies of sensory neurons.

Anterior ramus

Largest branch of a spinal nerve; often forms plexuses supplying limbs and anterior trunk.

Posterior ramus

Small branch of a spinal nerve serving muscles and skin of the back.

Rami communicantes

Pair of small branches carrying autonomic (sympathetic) fibers between spinal nerves and sympathetic trunk ganglia.

Dermatome

Cutaneous segment innervated by a single spinal nerve; useful for locating spinal injuries.

Plexus

Interlacing network of anterior rami that redistribute nerve fibers to form peripheral nerves.

Cervical plexus

Neck plexus formed by C1–C5; gives rise to the phrenic nerve.

Phrenic nerve

Motor nerve to the diaphragm; essential for breathing.

Brachial plexus

Plexus formed by C5–T1; supplies the upper limb.

Axillary nerve

Brachial-plexus branch; motor to deltoid/teres minor, sensory for shoulder skin.

Musculocutaneous nerve

Motor to biceps brachii and brachialis; sensory for lateral forearm.

Radial nerve

Motor to extensor muscles of arm and forearm; sensory to posterior limb and hand.

Median nerve

Motor to lateral forearm flexors; sensory to lateral palm and fingers; compressed in carpal tunnel syndrome.

Ulnar nerve

Motor to medial forearm flexors; sensory to medial hand; struck at the ‘funny bone.’

Referred pain

Perception of pain in a region other than the stimulus source (e.g., elbow strike felt in hand).