2Y03 NERVOUS SYSTEM, CELLS, AND NERVES

lectures 9, 10, 11, 12, 13

functions of the nervous system

sense changes through the sensory receptors, respond to stimuli, analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviours

central nervous system (CNS)

brain and spinal cord

peripheral nervous system (PNS)

sensory receptors and nerves (cranial and spinal nerves)

sensory receptors

ending of neurons or separate, specialized cells that detect things such as temperature, pain, etc. taking information from the outside world

nerve

a bundle of axons and their sheaths that connects CNS to sensory receptors, muscles, and glands

cranial nerves

originate from the brain; 12 pairs (bilateral)

spinal nerves

originate from the spinal cord; 31 pairs

ganglion

collection of neuron cell bodies outside CNS

plexus

extensive network of axons, and sometimes neuron cell bodies, located outside CNS

sensory division of PNS

afferent; transmits action potentials from receptors to CNS

motor division of PNS

efferent; transmits action potentials from CNS to effectors (muscles and glands)

general senses

receptors throughout the body (ex. skin → temperature and pressure)

special senses

receptors in specific organs, very specialized (ex. vision → light detection)

somatic nervous system

CNS to skeletal muscles; voluntary control, single neuron system (short/long)

synapse with skeletal muscle

junction of a nerve cell with another cell (ex. neuromuscular junction is a synapse between a neuron and a skeletal muscle cell)

autonomic nervous system (ANS)

from CNS to smooth muscle, cardiac muscle, and certain glands; involved in involuntary control & two neuron system

two neuron system

first from CNS to ganglion; second from ganglion to effector

divisions of ANS

sympathetic and parasympathetic

sympathetic nervous system

prepares body for physical activity (fight-or-flight)

parasympathetic nervous system

regulates resting or vegetative functions such as digesting food (rest and digest)

enteric nervous system (ENS)

plexuses within the wall of the digestive tract. can control the digestive tract indepedently of the CNS but still communicates with the CNS via the ANS (ex. the brain doesn’t always need to know whats going on to function); stretches walls from chemical signals and contracts smooth muscles/controls secretions

neurons or nerve cells

receive stimuli and transmit action potentials to other neurons or effector organs

neuroglia or glial cells

non-neural cells, support and protect neurons

dendrites

short extensions of the cell body — input part of the neuron, can interact with axons of other neurons

axons

arise at the cone shaped area of the neuron “hillock”, starting area called inital segment (both make up the trigger zone) diameter is constant but the length can vary up to 1m

axoplasm

the cytoplasm of an axon

axolemma

the membrane of an axon

terminal end

presynaptic terminal or synaptic end bulb

vesicles

neurotransmitters — a type of axonal transport; found in the presynaptic terminal, can release neurotransmitters to stimulate or inhibit a postsynaptic cell, can move up and down an axon

axonal transport

mainly through vesicles/neurotransmitters, stimulate or inhibits other postsynaptic cells, also the way disease can be transmitted to the CNS (ex. rabies or herpes)

sensory or afferent

action potentials towards the CNS

motor or efferent

action potentials away from the CNS

interneurons or association neurons

direction of nerve impulse; within the CNS from one neuron to another

multipolar neuron

many dendrites, single axon — most common neuron in the CNS and motor neurons

bipolar neuron

1 dendrite, 1 axon — found in sensory organs (ex. eye → highly specialized areas)

pseudo-unipolar neuron

single process extending from the cell body — divides into two branches, part extends to periphery has dendrites that typically function as sensory receptors

neuroglia

numerous (account for over 50% of the weight of brain), 4 different types in the CNS, 2 types in PNS, unique structure and function

astrocytes

found in the CNS, star shaped, cytoplasmic extension branch to form foot processes — cover the surface of blood vessels, neurons, pia mater; release chemicals from tight junctions between endothelial cells of capillaries; in the blood brain barrier

blood brain barrier

protects against toxic substances

ependymal cells

CNS: lines the ventricles of the brain and central canal of the spinal cord, helps form the choroid plexus — produces CSF, patches contain cilia; help move CSF through ventricles

microglia

CNS: specialized macrophages in the CNS, phagocytic — inflammation; wrap around foreign objects, dying tissue, and microorganisms and digest them

oligodendrocytes

found in the CNS: cytoplasmic extensions that surround axons, form the myelin sheath around portions of several axons

schwann cells

found in PNS: wrap around axons, forms the myelin sheath around a portion of only one axon

satellite cells

found in the PNS: surround neuron cell bodies in ganglia, provides nutrients to cell body (protection)

myelin

protects and insulates axons from one another, allows axons to conduct signals more rapidly

myelinated axon

unmyelinated axon

tract

bundle of unmyelinated axons in the CNS

nucleus

collection of neuron cell bodies in the CNS

white matter

myelinated axons; nerve tracts propagate AP from one area in the CNS

gray matter

unmyelinated axons, cell bodies, dendrites, neuroglia; integrative functions

spinal cord matter

white is outer, gray is deeper

brain matter

gray is outer cortex as well as inner nuclei; white is deeper

brainstem

connects spinal cord to brain; integration of reflexes necessary for survival

cerebellum

involved in control of locomotion, balance, and posture; 50% of the brains neurons

diencephalon

consists of the thalamus, epithalamus, hypothalamus, and subthalamus; deep above brainstem

brain protection

cranial bones (skull), cranial meninges, and cerebrospinal fluid

cranial meniges

pia, arachnoid, and dura mater (2 layers: meningeal dura and periosteal dura)

cerebrospinal fluid (CSF)

serum-like fluid lacking proteins but containing nutrients; bathes and protects the brain and spinal cord; mostly synthesized in the choroid plexus — lateral ventricles

brainstem components

medulla oblongata, pons, midbrain

medulla oblongata

transmits ascending and descending impulses between brain and spinal cord, center for vital reflexes (heart rate, BP, respiration, swallowing, coughing, & sneezing); houses cranial nerves V, VII, IX, X, XI, XII

pyramids

part of the medulla oblongata; nerve tracts that involve conscious control of skeletal muscle, they decussate (cross/intersect in X shape) and are only descending

olives

part of the medulla oblongata; nuclei involved in balance, coordination, modulation of sound; it does this by redirecting sensory information from muscles to joints to the cerebellum

pons

ascending and descending nerve tracts, functions include the sleep center and respiratory center (REM), anterior contains pontine nuclei, posterior contains cranial nerves V,VI, VII, VIII

pontine nuclei

communication between cerebrum and cerebellum

midbrain

most superior part of brainstem, houses cranial nerves III, IV, V, and tectum

tectum

4 nuclei that form molds on the dorsal surface of midbrain; each part houses a colliculus

superior colliculi

part of the tectum, involved in visual processing

inferior colliculi

part of the tectum, involved in hearing

reticular formation

group of nuclei scattered throughout brainstem, “cloud”, controls cyclic activities such as sleep-wake cycle

cerebellum

communicates with other regions of the CNS: midbrain (superior cerebellar peduncle), pons (middle cerebellar peduncle) and medulla oblongata (inferior cerebellar peduncle)

three main regions: flocculonodular lobe, vermis, and cerebellar

flocculondular lobe

regions within the cerebellum involved in balance

vermis

region in the cerebellum involved in gross motor coordination (anterior) and fine motor coordination (posterior)

cerebellar

region of the cerebellum, involved in fine motor coordination