xiv. nervous system

acetylcholine

neurotransmitter chemical released at the ends of nerve cells

afferent nerve

carries messages toward the brain and spinal cord (sensory nerve)

arachnoid membrane

middle layer of the three membranes (meninges) that surround the brain and spinal cord; loosely attached to other meninges by web-like fibers, so there is space for fluid between the fibers and third membrane

astrocyte

type of glial (neuroglial) cell that transports water and salts from capillaries in the nervous system

autonomic nervous system

nerves that control involuntary body functions of muscles, glands, and internal organs

axon

microscopic fiber that is part of a neuron and carries nervous impulse along a nerve cell

blood brain barrier (BBB)

protective separation between the blood and brain cells; this makes it difficult for substances (such as anticancer drugs) to penetrate capillary walls and enter the brain

brainstem

posterior portion of the brain that connects the cerebrum with the spinal cord; includes the midbrain, pons, and medulla oblongata

cauda equina

collection (fan) of spinal nerves below the end of the spinal cord

cell body

part of a nerve cell that contains the nucleus

central nervous system (CNS)

brain and spinal cord

cerebellum

posterior part of the brain that coordinates muscle movements and maintains balance

cerebral cortex

outer surface region of the cerebrum, containing sheets of nerve cells; gray matter of the brain

cerebrospinal fluid (CSF)

circulates throughout the brain and spinal cord; protects the brain and spinal cord from shock by acting like a cushion; contains lymphocytes, sugar, and proteins

cereberum

largest part of the brain; responsible for voluntary muscular activity, vision, speech, taste, hearing, thought, and memory

cranial nerves

nerves carry messages to and from the brain to all parts of head and neck and also (in the case of the vagus nerve) to other parts of the body; there are 12 pairs

dendrite

microscopic branching fiber of a nerve cell (neuron) that is the first part to receive the nervous impulse

dura mater

thick, tough, outermost layer of the meninges surrounding and protecting the brain and spinal cord; outer region; containing nerve fiber tracts w myelin sheaths; conducting impulses to + from brain

efferent nerve

carries messages away from the brain and spinal cord; motor nerve

ependymal cell

glial cell that lines membranes within the brain and spinal cord and helps form cerebrospinal fluid

ganglion (plural: ganglia)

collection of nerve cell bodies in the peripheral nervous system

glial cell (neuroglial cell)

supportive and connective nerve cell that does not carry nervous impulses; examples are astrocytes, microglial cells, ependymal cells, and oligodendrocytes; can reproduce themselves

gyrus (plural: gyri)

sheet of nerve cells that produces a rounded ridge on the surface of the cerebral cortex; convolution

hypothalamus

portion of the brain beneath the thalamus; controls sleep, appetite, body temperature, and secretions of hormones from the pituitary gland

medulla oblongata

part of the brain just above the spinal cord; controls breathing, heartbeat, and the size of blood vessels; nerve fibers cross over here”

meninges

three protective membranes that surround the brain and spinal cord

microglial cell

phagocytic glial cell that removes waste products from the central nervous system

midbrain

uppermost portion of the brainstem; contains pathways connecting the cerebrum with lower portions of the brain, and structures involved with seeing and hearing

motor nerve

carries messages away from the brain and spinal cord to muscles and organs; efferent nerve

myelin sheath

covering of white fatty tissue that surrounds and insulates the axon of a nerve cell; speeds impulse conduction along axons

nerve

macroscopic cord-like collection of fibers (axons) that carry electrical impulses

neuron

nerve cell that is necessary for impulses to be carried throughout the nervous system; parenchyma of the nervous system

neurotransmitter

chemical messenger released at the end of a nerve cell. It stimulates or inhibits another cell, which can be a nerve cell, muscle cell, or gland cell; examples are acetylcholine, norepinephrine, dopamine, and serotonin

oligodendroglial cell

glial cell that forms the myelin sheath covering axons; also called oligodendrocyte

parasympathetic nerves

involuntary autonomic nerves that regulate normal body functions such as heart rate, breathing, and muscles of the gastrointestinal tract

parenchyma

essential, distinguishing tissue of any organ or system

peripheral nervous system

nerves outside the brain and spinal cord: cranial, spinal, and autonomic nerves

pia mater

thin, delicate inner (third) membrane of the meninges; contains delicate connective tissue with rich supply of blood vessels

plexus (plural: plexuses)

large, interlacing network of nerves; examples are lumbosacral, cervical, and brachial

pons

part of the brain anterior to the cerebellum and between the medulla and the rest of the midbrain; it is a bridge connecting various parts of the brain

receptor

organ that receives and transmits a stimulus to sensory nerves; examples are the skin, ears, eyes, and taste bud

sciatic nerve

n“Nerve extending from the base of the spine down the thigh, lower leg, and foot

sciatica

pain or inflammation along the course of the sciatic nerve

sensory nerve

carries messages toward the brain and spinal cord from a receptor; afferent nerve

spinal nerves

pairs of nerves, arising one on each side of the spinal column; they transmit messages to and from the spinal cord

stimulus (plural: stimuli)

agent of change in the internal or external environment that evokes a response; it may be light, sound, touch, pressure, or pain

stroma

connective and supporting tissue of an organ; glial cells make up this type of tissue of the brain

sulcus (plural: sulci)

depression or groove in the surface of the cerebral cortex; fissure

sympathetic nerves

autonomic nerves that influence bodily functions involuntarily in times of stress

synapse

space through which a nervous impulse travels between nerve cells or between nerve and muscle or glandular cells

thalamus

main relay center of the brain; it conducts impulses between the spinal cord and the cerebrum; incoming sensory messages are relayed through it to appropriate centers in the cerebrum

vagus nerve

tenth cranial nerve (cranial nerve X); its branches reach to the larynx, trachea, bronchi, lungs, aorta, esophagus, and stomach; unlike the other cranial nerves, it leaves the head and “wanders” into the abdominal and thoracic cavities

ventricles of the brain

canals in the brain that contain cerebrospinal fluid

demyelination

loss of myelin insulating a nerve fiber; characteristic of multiple sclerosis

cerebrum

largest part of the brain; responsible for voluntary muscular activity, vision, speech, taste, hearing, thought, and memory

lumbar puncture (LP)

spinal fluid is withdrawn for diagnosis or relief of pressure on the brain; a hollow needle inserted into the lumbar region of spinal column below where the nervous tissue of the spinal cord ends, and CSF withdrawn

respiratory centre

vital centre of the medulla oblongata that controls the muscles of respiration in response to chemicals or stimuli

cardiac centre

vital centre of the medulla oblongata that slows heart rate when the heart is beating too rapidly

vasomotor centre

vital centre of the medulla oblongata that affects (constricts or dilates) muscles in the walls of blood vessels, influencing blood pressure

basal ganglia

group of cells that regulate intentional movements of the body

corpus callosum

structure in the center of the brain and connects the two hemispheres

gray matter

inner region of the spinal cord; containing cell bodies + dendrites

white matter

outer region of the spinal cord; contain nerve fiber tracts with myelin sheaths; conduct impulses to and from the brain

central canal

space through which CSF travels

subdural hematoma

collection of blood below the dura mater; results from tearing of veins between the dura and arachnoid membranes; result of blunt trauma (ex. blows to head in boxers or in elderly patients fallen out of bed)

intracerebral hematoma

collection of blood within the cerebral caused by bleeding directly into brain tissue (ex. in uncontrolled hypertension)

chronic traumatic encephalopathy (CTE)

progressive degenerative disease associated with repetitive brain trauma (concussion)

gliomas

tumors of glial (neuroglial) cells

glioblastoma

highly malignant tumor of immature glial cells

leptomeninges

pia and arachnoid membranes; thin, delicate

meningioma

slow-growing benign tumor of meninges

myelomeningocele

neural tube defect caused by failure of neural tube to close during embryonic development; in infants born with spina bifida

poliomyelitis

viral disease that affects the gray matter of the spinal cord, leading to paralysis of muscles that rely on damaged neurons

sciatica radiculopathy

disease affecting the sciatic nerve in the back; herniated disc is the common cause leading to pain, weakness, or numbness down leg

trigeminal neurolgia

that involves flashes of pain radiating along the course of the trigeminal nerve (fifth cranial nerve)

cephalgia

headache; may result from tension in the neck and scalp muscles

causalgia

intense burning pain following an injury to sensory nerve

coma

state of unconsciousness from which a patient cannot be aroused

semicomatose

unresponsiveness from which a patient can be aroused

irreversible coma (brain death)

complete unresponsitivity, no spontaneous breathing or movement, and flat electrocencephalogram (EEG)

anesthesia

lack of normal sensation (ex. absence of sense of touch or pain)

anesthesiologist

physician who administers anesthesia

anesthetics

agents that reduce or eliminate sensation (general or local)

epidural (caudal) anesthesia

done by injecting an agent into the epidural space, commonly in obstetrics

spinal anesthesia

done by injecting local anesthetic into the subarachnoid space

hyperesthesia

abnormally intense sensation to a particular stimulus (ex. light tough with a pin)

hypesthesia

diminished sensitivity to pain

paraesthesia

abnormal feeling; including tingling, burning, and ‘pins and needles’ sensations

tardive (occurring late) dyskinesia

abnormal movement that may develop in people who receive certain antipsychotic drugs for extended periods; marked by involuntary, spasmodic movements

narcolepsy

sudden, uncontrollable compulsion to sleep

dyslexia

developmental reading disorder when the brain does not properly recognize, process, and interpret language

motor (Broca or expressive) aphasia

patients know what they want to say but cannot say it

sensory aphasia

patients have difficulty understanding language and may pronounce (articulate) words easily but use them inappropriately

hemiplegia

paralysis that affects the right or left half of body and results from stroke or other brain injury; contralateral to the brain lesion because of motor nerve fibers from right half of brain cross to left side of body, vice versa (in medulla oblongata)

paraplegia

paralysis of both legs and lower part of the body caused by injury or disease of the spinal cord or cauda equina

quadriplegia

paralysis in which all four extremities are affected; due to an injury at the cervical level of the spinal cord

apraxia

when movements and behavoiur are not purposeful

neurasthenia

nervous exhaustion and fatigue, often following depression

syncope

fainting; sudden and temporary loss of consciousness caused by inadequate flow of blood to the brain

ataxia

persistent unsteadiness on one’s feet; can be caused by a disorder involving the cerebellum