Nervous System & Brain Anatomy Lecture

Nervous System

Organ system composed of brain, spinal cord, nerves, ganglia and nervous tissue that performs sensory input, information processing/integration, and motor output.

Central Nervous System (CNS)

Brain and spinal cord; the main processing and integrating centers of the nervous system.

Peripheral Nervous System (PNS)

All nerves and ganglia outside the CNS; connects the CNS to the rest of the body.

Sensory Function

Detection of internal or external stimuli and transmission of that information to the CNS.

Processing / Integrating Function

CNS activity that interprets sensory information and decides on responses.

Motor Function

Activation of effectors (muscles or glands) to produce a response based on CNS commands.

Neuron

Electrically excitable cell that transmits action potentials.

Nerve

Bundle of axons in the PNS wrapped in connective tissue layers.

Dendrite

Branch-like neuronal process that receives input and conveys it to the cell body.

Cell Body (Soma)

Central part of a neuron containing the nucleus and most organelles.

Axon

Long neuronal process that conducts action potentials away from the cell body to synaptic knobs.

Synaptic Knob

Bulbous axon ending that releases neurotransmitter into the synaptic cleft when an action potential arrives.

Graded Potential

Small, localized change in membrane potential occurring in dendrites or soma; can depolarize or hyperpolarize.

Action Potential

All-or-none electrical impulse generated at the axon hillock and propagated along the axon.

Multipolar Neuron

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

Bipolar Neuron

Neuron with one dendrite and one axon; found in special senses such as retina and olfactory epithelium.

Unipolar Neuron

Neuron with a single process that splits into peripheral and central branches; most sensory neurons.

Epineurium

Dense irregular connective tissue that encloses the entire nerve for protection and support.

Perineurium

Dense irregular connective tissue that surrounds each fascicle and supports blood vessels.

Endoneurium

Areolar connective tissue that wraps each axon, providing separation and electrical insulation.

Oligodendrocyte

CNS glial cell that myelinates and insulates CNS axons, speeding signal propagation.

Astrocyte

CNS glial cell that forms the blood–brain barrier, regulates interstitial fluid, provides structural support, and fills spaces of dying neurons.

Ependymal Cell

CNS glial cell lining ventricles and central canal; produces and circulates cerebrospinal fluid.

Microglial Cell

Small CNS phagocyte that removes debris, pathogens, and unnecessary synapses.

Satellite Cell

PNS glial cell that electrically insulates somas in ganglia and regulates nutrient/waste exchange.

Neurolemmocyte (Schwann Cell)

PNS glial cell that myelinates and insulates PNS axons to speed conduction.

Myelin Sheath

Concentric layers of glial plasma membrane around an axon that act as electrical insulation.

Wallerian Degeneration

Breakdown of distal axon and myelin after injury, followed by phagocytosis and potential regeneration.

Resting Membrane Potential (RMP)

Baseline electrical charge across the plasma membrane, approximately –70 mV in neurons.

All-or-None Law

Principle that an action potential is generated only if threshold is reached; its size is not graded.

Absolute Refractory Period

Time during which a neuron cannot be re-stimulated because voltage-gated Na⁺ channels are inactivated.

Relative Refractory Period

Period immediately after the absolute phase when a stronger-than-normal stimulus can initiate another action potential.

Excitatory Postsynaptic Potential (EPSP)

Depolarizing graded potential that brings the postsynaptic membrane closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

Hyperpolarizing graded potential that moves the postsynaptic membrane farther from threshold.

Summation

Additive effect of EPSPs and IPSPs at the initial segment determining whether threshold is reached.

Spatial Summation

Simultaneous stimulation of a postsynaptic neuron by multiple presynaptic neurons.

Temporal Summation

Rapid, repeated stimulation of a postsynaptic neuron by one presynaptic neuron.

Continuous Conduction

Sequential opening of Na⁺ and K⁺ channels along an unmyelinated axon.

Saltatory Conduction

Jumping of an action potential from node to node along a myelinated axon, increasing speed.

Chemical Synapse

Junction where a neurotransmitter is released from a presynaptic neuron to influence a postsynaptic cell.

Neurotransmitter

Chemical messenger released by neurons that crosses a synapse to stimulate or inhibit another cell.

Neurotransmitter Receptor

Protein on the postsynaptic membrane that binds neurotransmitter and initiates a cellular response.

Acetylcholine

Widely used neurotransmitter in CNS and PNS; excites skeletal muscle and has varied autonomic effects.

Biogenic Amines

Neurotransmitters derived from amino acids, including catecholamines and indolamines.

Catecholamines

Dopamine, norepinephrine, and epinephrine; a subgroup of biogenic amines derived from tyrosine.

Amino Acid Neurotransmitters

Glutamate, aspartate, serine, glycine, and GABA; simple amino acids acting as synaptic messengers.

Neuropeptides

Chains of 2–40 amino acids, e.g., β-endorphin, functioning as neurotransmitters or neuromodulators.

Neural Circuit (Neuronal Pool)

Functional grouping of interneurons that process specific types of information.

Converging Circuit

Neural arrangement where multiple inputs synapse on a single postsynaptic neuron.

Diverging Circuit

Neural arrangement in which one presynaptic neuron spreads impulses to many neurons or pools.

Cranial Meninges

Three connective tissue layers (pia, arachnoid, dura) that protect and support the brain.

Pia Mater

Thin, areolar connective tissue layer adherent to the brain surface.

Arachnoid Mater

Web-like middle meningeal layer between pia and dura mater.

Subarachnoid Space

Area between arachnoid and pia mater that contains cerebrospinal fluid.

Dura Mater

Tough, outermost meningeal layer that protects the brain and forms dural sinuses.

Cerebrospinal Fluid (CSF)

Clear fluid circulating in ventricles, subarachnoid space, and central canal for buoyancy, protection, and chemical stability.

Choroid Plexus

Specialized capillary-ependymal complex in each ventricle that forms CSF from filtered blood plasma.

Blood–Brain Barrier (BBB)

Selective barrier formed by brain capillary endothelia and astrocytes that limits passage of substances from blood to brain tissue.

Cerebrum

Largest brain region; site of conscious thought, sensory perception, voluntary motor activities, and complex cognition.

Frontal Lobe

Anterior cerebral lobe involved in voluntary motor control, planning, personality, and speech production.

Parietal Lobe

Superior-posterior cerebral lobe processing general sensory input and body position.

Temporal Lobe

Lateral cerebral lobe concerned with hearing and smell.

Occipital Lobe

Posterior cerebral lobe devoted to visual processing and visual memory storage.

Insula

Deep cerebral lobe involved in taste and memory.

Gyrus (plural: Gyri)

Elevated ridge or fold on the cerebral cortex.

Corpus Callosum

Major white-matter tract that connects the left and right cerebral hemispheres.

Cerebral Cortex

Outer layer of gray matter on the cerebrum responsible for higher cognitive functions and voluntary movement.

Diencephalon

Brain region composed of thalamus, hypothalamus, and epithalamus located deep to the cerebrum.

Epithalamus

Posterior roof of diencephalon containing the pineal gland and habenular nuclei.

Pineal Gland

Epithalamic endocrine gland that secretes melatonin to regulate circadian rhythms.

Habenular Nuclei

Epithalamic structures relaying emotional responses from the limbic system to the midbrain.

Thalamus

Paired diencephalic relay station for sensory information and contributor to motor control.

Hypothalamus

Diencephalic region that controls autonomic and endocrine functions, body temperature, hunger, thirst, and emotions.

Optic Chiasma

X-shaped region where optic nerves partially cross, allowing visual input from both eyes to reach both hemispheres.

Cerebellum

Second-largest brain region that coordinates movement, balance, and posture.

Cerebellar Hemispheres

Left and right lateral portions of the cerebellum.

Arbor Vitae

Tree-like pattern of internal cerebellar white matter.

Brainstem

Connective stalk comprising midbrain, pons, and medulla oblongata linking higher brain regions to the spinal cord.

Midbrain

Superior part of brainstem involved in visual and auditory reflexes and motor control.

Pons

Bulging middle brainstem region containing respiratory centers and fiber tracts.

Medulla Oblongata

Inferior brainstem region regulating heart rate, blood pressure, and respiration; conduit between spinal cord and higher centers.

Primary Somatosensory Cortex

Postcentral gyrus region that receives and processes general somatic sensory information.

Somatosensory Association Area

Parietal lobe area posterior to the postcentral gyrus that interprets sensory characteristics like texture and shape.

Primary Visual Cortex

Occipital lobe area that receives basic visual input from the retina.

Visual Association Area

Occipital region surrounding the primary visual cortex that interprets and gives meaning to visual stimuli.

Primary Auditory Cortex

Temporal lobe area receiving auditory information from the ear.

Auditory Association Area

Temporal lobe region that interprets sound characteristics and stores auditory memories.

Primary Motor Cortex

Precentral gyrus region controlling voluntary skeletal muscle activity.

Motor Speech Area (Broca’s Area)

Inferolateral portion of left frontal lobe that coordinates muscles for vocalization.

Tract

Bundle of myelinated axons within the CNS connecting different brain or spinal cord regions.

Limbic System

Group of cerebral and diencephalic structures involved in emotion, motivation, and memory.

Reticular Activating System (RAS)

Part of reticular formation that maintains cortical alertness by processing sensory input.

Sensory Memory

Very brief storage of sensory information lasting milliseconds to 1 second.

Short-Term Memory (STM)

Temporary information storage with limited capacity lasting about 1 minute.

Long-Term Memory (LTM)

Relatively permanent and limitless store of information.

Olfactory Nerve (I)

Cranial nerve for sense of smell.

Optic Nerve (II)

Cranial nerve conveying visual information from the retina.

Oculomotor Nerve (III)

Cranial nerve that innervates four extrinsic eye muscles and controls pupil constriction.

Trochlear Nerve (IV)

Cranial nerve that innervates the superior oblique muscle of the eye.

Trigeminal Nerve (V)

Cranial nerve providing facial somatic sensation and innervating muscles of mastication.