anatomy exam 4

functions of the nervous system

communication and coordination, site of reasoning (brain)

two main divisions of nervous system

central nervous system and peripheral nervous system

neuron

basic structural unit of the nervous system

dendrites

motor neurons can contain 100s of these tapering, diffusing branched processes. contain same organelles as in cell body. receptive region of neuron. convey incoming messages toward cell body as graded potentials

axon

carry impulses away from the cell

sensory (afferent) neurons

carry nerve impulse/ message from a stimulus to brain

motor (efferent) neurons

carry nerve impulse/message from brain to muscle

central nervous system

brain and spinal cord, integration and control center. interprets sensory input and dictates motor output

cerebrum

largest part of brain, responsible for reasoning, thought, memory, speech, sensation. divided into 2 halves and into 4 lobes

cerebellum

11% of brain mass, located dorsal to pons and medulla, processes input from cortex, brain stem, and sensory receptors to provide smooth coordinated movements

brain stem

most basic functions; respiration, swallowing, blood pressure. lower part is continuous with spinal cord

spinal cord

begins at foramen magnum and ends at second lumbar vertebrae. contains afferent and efferent neurons

afferent

to the brain

efferent

away from the brain

meninges

protective membranes that cover the brain and spinal cord

ventricles

four fluid-filled cavities within the brain. continuous to one another and to central canal of spinal cord

cerebrospinal fluid

produced in the ventricles, bates the brain and spinal cord

peripheral nervous system

the portion of nervous system outside CNS, consists mainly of nerves that extend from brain and spinal cord

spinal nerves

to and from spinal cord

cranial nerves

to and from brain

2 parts of peripheral nervous system

somatic and autonomic

somatic nervous system

carries sensory and motor information to and from the central nervous system

autonomic nervous system

responsible for regulating involuntary body functions, such as blood flow, heartbeat, digestion, and breathing

somatic system

12 pairs cranial nerves, 31 pairs spinal nerves

autonomic system

sympathetic and parasympathetic

how do cells communicate in the nervous system

via electrical and chemical signals. rapid and specific, usually cause almost immediate responses

sensory input

information gathered by sensory receptors about internal and external changes

integration

processing and interpretation of sensory input

motor output

activation of effector organs (muscles and glands) produces a response

two functional divisions of PNS

sensory (afferent) and motor (efferent)

sensory (afferent) division

somatic sensory fibers and visceral sensory fibers

somatic sensory fibers

convey impulses from skin, skeletal muscles, and joints to CNS

visceral sensory fibers

convey impulses from visceral organs to CNS

motor (efferent) division

transmits impulses from CNS to effector organs (muscles and glands). 2 divisions are somatic nervous system and autonomic nervous system

motor division of PNS: somatic nervous system

somatic motor nerve fibers, conducts impulses from CNS to skeletal muscle. voluntary nervous system (conscious control of skeletal muscles)

motor division of PNS: autonomic nervous system

visceral motor nerve fibers, regulates smooth muscle, cardiac muscle, and glands. involuntary nervous system

two functional subdivisions of autonomic nervous system

sympathetic and parasympathetic (work in opposition to eachother)

histology of nervous tissue

highly cellular, little extracellular space. two principal cell types are neuroglia and neurons

neuroglia

small cells that surround and wrap delicate neurons

neurons (nerve cells)

excitable cells that transmit electrical signals

neuroglia cells of the CNS

astrocytes, microglial cells, ependymal cells, oligodendrocytes

neuroglia cells of the PNS

satellite cells and schwann cells

astrocytes

most abundant, versatile, and highly branched glial cells. cling to neurons, synaptic endings and capillaries

functions of astrocytes

support and brace neurons, play role in exchanges between capillaries and neurons, respond to nerve impulses and neurotransmitters and influence neuronal functioning

microglial cells

small, ovoid cells with thorny processes that touch and monitor neurons. migrate towards injured neurons and can transform to phagocytize microorganisms and neuronal debris

ependymal cells

range in shape from squamous to columnar, may be ciliated (cilia beat to circulate CSF), line the central cavities of the brain (ventricles) and spinal column

oligodendrocytes

branched cells, processes wrap CNS nerve fibers, forming insulating myelin sheaths

satellite cells

surround neuron cel bodies in PNS, function similar to astrocytes of CNS

schwann cells

surround all peripheral nerve fibers and from myelin sheaths in thicker nerve fibers. similar function to oligodendrocytes

neurons

structural units of nervous system, large highly specialized cells that conduct impulses. amitotic, high metabolic rate that requires continuous supply of blood and glucose. all have cell body and one or more processes

neuron cell body (soma)

biosynthetic center of neuron, spherical nucleus with nucleolus. plasma membrane part of receptive region that receives input from other neurons. most located in CNS

biosynthetic center of neuron

synthesizes proteins, membranes and other chemicals. rough ER (nissl bodies) most active and best developed in the body

nuclei

clusters of neuron cell bodies in CNS

ganglia

lie along nerves in PNS

neuron processes

armlike processes that extend from cell body

neuron processes in CNS

contains both neuron cell bodies and their processes

neuron processes in PNS

contains chiefly neuron processes

tracts

bundles of neuron processes in CNS

nerves

bundles of neuron processes in PNS

two types of processes

dendrites and axon

axon structure

each neuron has one axon that starts at cone-shaped area called axon hillock. some are short and some can be over 1 meter long. branch profusely at their end (terminus)

long axons are called

nerve fibers

axon collaterals

occasional branches of axons

axon terminals

distal endings, secretory region

functional characteristics of axon

conducting region of neuron, generates nerve impulses, transmits them along axolemma to axon terminal

axolemma

neuron cell membrane

neurotransmitters

released into extracellular space, either excite or inhibit neurons which axons in close contact

transport along the axon

molecules and organelles are moved along axons (by motor proteins and cytoskeletal elements) movement in both directions

anterograde

away from the cell body

retrograde

toward cell body

myelin sheath

composed of myelin, whitish protein-lipid substance. segmented sheath around most long or large diameter axons (myelinated fibers)

function of myelin

protects and electrically insulates axon, increases speed of nerve impulse transmission

nonmyelinated fibers

conduct impulses more slowly

myelination in the PNS

formed by schwann cells- wrap around axon in jelly roll fashion, one cell formes one segment of myelin sheath. myelin sheath and outer collar of perinuclear cytoplasm

nodes of ranvier

myelin sheath gaps between adjacent schwann cells. sites where axon collaterals can emerge

plasma membranes of myelinating cells have less

protein- no channels or carriers, good electrical insulators

myelin sheaths in the CNS

formed by multiple, flat processes of oligodendrocytes, not whole cells. can wrap up to 60 axons at once, nodes of ranvier are present, no outer collar of perinuclear cytoplasms, thinnest fibers unmyelinated. has white and gray matter

white matter

regions of brain and spinal cord with dense collections of myelinated fibers- usually fiber tracts. nonmyelinated axons

gray matter

short, mostly neuron cell bodies and nonmyelinated fibers

structural classification of neurons

multipolar, bipolar, unipolar

multipolar neuron

3 or more processes; 1 axon others dendrites. most common, major neuron in CNS

bipolar neuron

2 processes; 1 axon, 1 dendrite. rare ex: retina and olfactory mucosa

unipolar neuron

1 short process. divides t-like, both branches considered axons

distal (peripheral) process

unipolar process, associated with sensory receptor

proximal (central) process

unipolar process, enters CNS

functional classification of neurons

grouped by direction in which nerve impulse travels relative to CNS. 2 types are sensory (afferent) and motor (efferent)

sensory neurons

afferent neurons; transmit impulses from sensory receptors toward CNS. almost all are unipolar, cell bodies are ganglia in PNS

motor neurons

efferent neurons; carry impulses from CNS to effectors. multipolar, most cell bodies in CNS

cephalization

evolutionary development of rostral (anterior) portion of CNS, which resulted in increased number of neurons

embryologically, the brain and spinal cord begin as a

neural tube

how does the neural tube become spinal cord and brain

posterior end becomes spinal cord and anterior end expands, and constrictions form three primary vesicles: forebrain, midbrain and hindbrain

prosencephalon

forebrain

mesencephalon

midbrain

rhombencephalon

hindbrain

forebrain becomes

telencephalon and diencephalon

midbrain remains

undivided

hindbrain becomes

metencephalon and myelencephalon

telencephalon in development

gives rise to two cerebral hemispheres, together they make up the cerebrum

diencephalon in development

becomes the epithalamus, thalamus, hypothalamus and retina

mesencephalon in development

remains the midbrain