BIOL 220 - Unit 4: Nervous System, Spinal Cord & Brain (Lab Practical 3)

Neuron

The functional unit of the nervous system; conducts electrical signals (nerve impulses)

Cell body (soma)

Metabolic center of the neuron; contains nucleus and organelles

Dendrites

Short, branching processes of a neuron that receive signals and carry them TOWARD the cell body

Axon

Single long process that carries impulses AWAY from the cell body

Axon hillock

Cone-shaped region of the cell body where the axon originates; site of action potential initiation

Myelin sheath

Insulating layer of lipid-rich material surrounding axons; speeds up nerve impulse conduction

Schwann cells

Neuroglia in the PNS that produce the myelin sheath around peripheral axons

Nodes of Ranvier

Gaps in the myelin sheath between Schwann cells; impulse jumps between nodes (saltatory conduction)

Synaptic terminals (axon terminals)

End bulbs at the tip of axon collaterals; release neurotransmitters into the synapse

Neuroglia (glial cells)

Support cells of the nervous system; do NOT transmit impulses

Astrocytes

Most abundant CNS glial cells; support neurons, maintain blood-brain barrier, regulate extracellular environment

Oligodendrocytes

CNS glial cells that produce myelin sheaths around CNS axons

Microglia

CNS glial cells; act as immune cells, phagocytize debris and pathogens

Ependymal cells

CNS glial cells that line ventricles and central canal; help circulate cerebrospinal fluid (CSF)

Satellite cells

PNS glial cells that surround neuron cell bodies in ganglia

Multipolar neuron

Neuron with many dendrites and one axon; most common type; includes motor neurons

Bipolar neuron

Neuron with one dendrite and one axon; found in special sense organs (retina, olfactory)

Unipolar (pseudounipolar) neuron

Neuron with one process that divides into two; most sensory neurons are this type

Afferent (sensory) neurons

Carry impulses FROM receptors TOWARD the CNS

Efferent (motor) neurons

Carry impulses FROM the CNS TOWARD effectors (muscles/glands)

Interneurons (association neurons)

Located entirely in CNS; connect sensory and motor neurons

CNS

Central Nervous System; consists of the brain and spinal cord

PNS

Peripheral Nervous System; consists of all nerves and ganglia outside the brain and spinal cord

Somatic nervous system

Division of PNS that controls voluntary skeletal muscle movements

Autonomic nervous system (ANS)

Division of PNS that controls involuntary activities (smooth muscle, cardiac muscle, glands)

Spinal cord

Part of CNS located within the vertebral canal; extends from foramen magnum to L1-L2

Conus medullaris

Tapered inferior end of the spinal cord; ends at L1-L2

Filum terminale

Slender connective tissue thread that anchors the spinal cord to the coccyx

Cauda equina

Bundle of spinal nerve roots below the conus medullaris; resembles a horse's tail

Cervical enlargement

Thickened region of spinal cord (C4-T1); gives rise to nerves supplying upper limbs

Lumbosacral enlargement

Thickened region of spinal cord (T9-T12/L1); gives rise to nerves supplying lower limbs

Gray matter (spinal cord)

H-shaped or butterfly-shaped central region of spinal cord; contains neuron cell bodies and unmyelinated axons

White matter (spinal cord)

Surrounds gray matter; consists of myelinated axon tracts

Dorsal horn

Posterior portion of gray matter; contains sensory (afferent) interneurons

Ventral horn

Anterior portion of gray matter; contains cell bodies of somatic motor neurons

Lateral horn

Found only in thoracic and upper lumbar segments; contains sympathetic preganglionic neurons

Dorsal root

Posterior root of spinal nerve; contains afferent (sensory) fibers entering the spinal cord

Dorsal root ganglion (DRG)

Swelling on the dorsal root containing cell bodies of sensory neurons

Ventral root

Anterior root of spinal nerve; contains efferent (motor) fibers leaving the spinal cord

Spinal nerve

Formed by the union of dorsal and ventral roots; mixed nerve containing both sensory and motor fibers

Dura mater

Outermost meninx; tough, fibrous connective tissue layer surrounding CNS

Arachnoid mater

Middle meninx; thin, web-like layer; subarachnoid space filled with CSF

Pia mater

Innermost meninx; delicate, highly vascular layer that adheres to surface of brain and spinal cord

Meninges

Three protective membranes covering the CNS: dura mater, arachnoid mater, pia mater

Cervical plexus

Network of spinal nerves C1-C4; supplies muscles and skin of neck and shoulder; gives rise to phrenic nerve

Phrenic nerve

Arises from cervical plexus (C3-C5); innervates the diaphragm

Brachial plexus

Network of spinal nerves C5-T1; supplies upper limb; gives rise to musculocutaneous, radial, median, ulnar, axillary nerves

Lumbar plexus

Network of spinal nerves L1-L4; supplies anterior and medial thigh; gives rise to femoral and obturator nerves

Sacral plexus

Network of spinal nerves L4-S4; supplies lower limb and gluteal region; gives rise to sciatic nerve

Sciatic nerve

Largest nerve in the body; arises from sacral plexus; runs down posterior thigh; divides into tibial and common fibular nerves

Dermatome

Area of skin innervated by sensory fibers from a single spinal nerve

Brainstem

Part of brain consisting of midbrain, pons, and medulla oblongata; connects brain to spinal cord

Medulla oblongata

Inferior part of brainstem; contains vital centers for heart rate, breathing, blood pressure; pyramids and decussation of pyramids

Pons

Middle part of brainstem; connects cerebellum to rest of brain; involved in breathing rhythm

Midbrain (mesencephalon)

Superior part of brainstem; contains corpora quadrigemina (superior and inferior colliculi) and cerebral peduncles

Superior colliculi

Part of midbrain; visual reflex centers (tracking moving objects, pupillary reflex)

Inferior colliculi

Part of midbrain; auditory reflex centers (startle reflex, sound localization)

Substantia nigra

Pigmented region of midbrain; involved in motor control; dopamine-producing neurons

Cerebral peduncles

Large fiber bundles on the anterior surface of midbrain; carry motor impulses from cerebrum to brainstem/spinal cord

Cerebellum

Located posterior to brainstem; coordinates skeletal muscle activity, balance, and posture; has two hemispheres with folia (folds)

Arbor vitae

Tree-like appearance of white matter in a sagittal section of the cerebellum

Cerebellar cortex

Outer gray matter of cerebellum; contains Purkinje cells

Diencephalon

Part of brain between brainstem and cerebrum; consists of thalamus, hypothalamus, and epithalamus

Thalamus

Largest part of diencephalon; main relay station for sensory information to cerebral cortex

Hypothalamus

Inferior to thalamus; regulates homeostasis, body temperature, hunger, thirst, sleep, and controls pituitary gland

Epithalamus

Superior to thalamus; includes pineal gland (melatonin secretion) and habenula

Pineal gland

Part of epithalamus; secretes melatonin to regulate circadian rhythms (sleep-wake cycle)

Cerebrum

Largest part of brain; divided into left and right hemispheres by the longitudinal fissure

Cerebral cortex

Outer gray matter of cerebrum; responsible for conscious thought, sensation, motor control

Cerebral white matter

Myelinated axons deep to the cortex; includes projection, association, and commissural fibers

Corpus callosum

Large band of commissural fibers connecting the two cerebral hemispheres

Frontal lobe

Anterior lobe of cerebrum; involved in voluntary motor control, speech, judgment, personality

Parietal lobe

Posterior to frontal lobe; processes general sensory information (touch, pressure, temperature)

Temporal lobe

Lateral lobe of cerebrum; involved in hearing, smell, memory, and language comprehension

Occipital lobe

Posterior lobe of cerebrum; processes visual information

Insula

Hidden lobe deep to lateral sulcus; involved in taste, visceral sensation, and interoception

Central sulcus

Groove separating frontal and parietal lobes; separates primary motor cortex from somatosensory cortex

Lateral sulcus (Sylvian fissure)

Groove separating frontal/parietal lobes from temporal lobe

Primary motor cortex

Located in precentral gyrus of frontal lobe; controls voluntary skeletal muscle movements

Primary somatosensory cortex

Located in postcentral gyrus of parietal lobe; receives and processes general sensory information

Broca's area

Located in frontal lobe (usually left hemisphere); controls speech production

Wernicke's area

Located in temporal lobe (usually left hemisphere); involved in language comprehension

Primary visual cortex

Located in occipital lobe; processes visual information

Primary auditory cortex

Located in temporal lobe; processes auditory information

Basal ganglia

Clusters of gray matter deep within cerebrum; involved in regulating movement and posture

Limbic system

Set of brain structures involved in emotion, memory, and motivation; includes hippocampus and amygdala

Hippocampus

Located in temporal lobe; essential for forming new long-term memories

Amygdala

Almond-shaped structure in temporal lobe; processes emotions, especially fear

Lateral ventricles

Large C-shaped cavities in each cerebral hemisphere; filled with CSF

Third ventricle

Cavity within the diencephalon between the two thalami; connected to lateral ventricles via interventricular foramina

Fourth ventricle

Cavity between pons/medulla and cerebellum; connected to third ventricle via cerebral aqueduct

Cerebrospinal fluid (CSF)

Clear fluid produced by choroid plexus in ventricles; cushions CNS, removes waste

Choroid plexus

Specialized capillary network in ventricles that produces CSF

Cranial nerve I - Olfactory

Sensory; smell (olfaction); arises from olfactory epithelium

Cranial nerve II - Optic

Sensory; vision; arises from retina

Cranial nerve III - Oculomotor

Motor; controls most eye movements (superior, inferior, medial rectus; inferior oblique); pupillary constriction; eyelid elevation

Cranial nerve IV - Trochlear

Motor; controls superior oblique muscle (moves eye downward and laterally)

Cranial nerve V - Trigeminal

Mixed; largest cranial nerve; three branches (ophthalmic, maxillary, mandibular); sensation of face; mastication muscles

Cranial nerve VI - Abducens

Motor; controls lateral rectus muscle (abducts eye)

Cranial nerve VII - Facial

Mixed; facial expression muscles; taste from anterior 2/3 of tongue; lacrimal/salivary gland secretion