Anatomy Test 3 Study Guide: Ch. 14, 15, 16, 18 & 20

Central Nervous System (CNS)

Contains brain and spinal cord

Peripheral Nervous System (PNS)

Contains nerves and ganglia

Neurons

excitable cells that generate, transmit, and receive nerve impulses

Glial Cells

non-excitable cells that support and protect neurons

Nerves

bundles of axons that carry signals to and from CNS (cranial nerves & spinal nerves)

Ganglia

clusters of neuron cell bodies

Know the 3 general functions of the nervous system

Collect information (sensory nervous system)
receptors
CNS processes and evaluates the information (determines response)
Initiate response to information (motor nervous system)
effectors

Receptors

detect changes from internal or external environment in PNS (stimuli) & send to CNS as sensory input

Effectors

after CNS selects appropriate response, sends motor output via nerve impulses (electrical charges) & motor output output travels here in the PNS

Examples of effectors in PNS

muscles & glands

Sensory Division (afferent)

(responsible for input) detects stimuli and transmits sensory information from receptors in PNS → CNS

2 components of sensory division (afferent)

somatic sensory & visceral sensory

Motor Division (efferent)

(responsible for output) motor output initiated and transmitted from CNS → effectors in PNS

2 components of motor division (efferent)

somatic motor (SNS) & autonomic motor (ANS)

Somatic Sensory

consciously perceive (voluntary) Ex’s

Visceral Sensory

usually not consciously perceive (involuntary) Ex’s

Somatic Motor

voluntary contractions and reflexes (consciously controlled) Ex

Autonomic (visceral) Motor

involuntary actions (not consciously controlled) Ex

Characteristics of neurons

excitable, conductivity, extreme longevity, amitotic, high metabolic rate

Excitable

respond to stimuli

Conductivity

propagates electrical charge

Secretory

releases neurotransmitters

Extreme longevity

most neurons from fetal development still functional in elderly

Amitotic

unable to divide, lose mitotic activity after fetal development (# of neurons after birth is your lifetime supply)

High Metabolic Rate

survival depends on continuous supply of glucose and oxygen

Cell Body

control center that receives, integrates, & sends nerve impulses

Dendrites

receive sensory input, then transfer input to cell body for processing

More dendrites = more information neurons can receive

Axon Hillock

triangular region where axon connects to cell body, initiates nerve impulse

Axon (nerve fiber)

transmits nerve impulses away from cell body, sends output information, & contacts other neurons, muscles, glands

Node of Ranvier

small gaps in myelin sheath, space where voltage can occur, speeds up signal conduction (“jumps” from node to node)

Synaptic Knob

slightly expanded regions at the ends of axon that forms synapses

Sensory Neurons (afferent)

detect stimuli (changes in environment) via receptors in PNS, then transmits sensory information to CNS

Interneurons (association neurons)

entirely within CNS, receive nerve impulses, integrate signals, and store information to determine how body responds, facilitate communication between sensory & motor neurons

Which neurons’ outnumber all other neurons’ by 99%?

Interneurons

Motor Neurons (efferent)

transmits motor commands from CNS to effectors (muscles or glands) in PNS

Unipolar Neuron

one short process that emerges from cell body like a “T” (sensory neurons)

Bipolar Neurons

2 processes- 1 axon & 1 dendrite (rare in humans, some olfactory and retinal neurons)

Multipolar Neurons

many dendrites & 1 axon (interneurons & motor neurons)

Most common neuron type (unipolar, bipolar, multipolar)

multipolar

Glial cells (neuroglia)

support, nourish, & protects neurons, capable of mitosis, 6 types

Astrocytes

most abundant in CNS (90%)

Astrocytes

form blood-brain-barrier (perivascular feet wrap around capillaries

Astrocytes

strictly controls what enters the neurons from blood, protects from toxins (wastes, drugs), but allows nutrients to pass in CNS

Astrocytes

regulate tissue fluid chemical composition

Astrocytes

strengthens & organizes nervous tissue

Astrocytes

replace damaged neurons

Astrocytes

directs neuron fetal growth

Astrocytes

regulate synaptic transmissions

Astrocytes Location (CNS or PNS)

CNS

Ependymal Cells

composed of ciliated simple cuboidal cells

Ependymal Cells

produces & circulates cerebral spinal fluid

Ependymal Cells

lines internal cavities of CNS (ventricles & central canal)

Ependymal Cells Location (CNS or PNS)

CNS

Microglial Cells

smallest % of CNS glial cells

Microglial Cells

phagocytic cells that remove debris from damaged/dead nervous tissue

Microglial Cells

wander through CNS multiple times a day & replicate in response to infection

Microglial Cells Location (CNS or PNS)

CNS

Oligodendrocytes

forms myelin sheaths around axons in CNS

Oligodendrocytes

arm-like processes spiral around axon

Oligodendrocytes Location (CNS or PNS)

CNS

Satellite Cells

surround neuron cell bodies to physically separate them in PNS ganglia

Satellite Cells

regulate exchange of nutrients & wastes in PNS

Satellite Cells Location (CNS or PNS)

PNS

Schwann Cells

form myelin sheaths to insulate axons in PNS

Schwann Cells Location (CNS or PNS)

PNS

Saltatory Conduction

nerve impulses travels down myelinated axons & produces a faster nerve impulse b/c action potential happens at neurofibril nodes (120 m/s)

Continuous Conduction

nerve impulses travels down unmyelinated axons & produces slower nerve impulse b/c action potential must travel down entire length of axon (2 m/s)

Speed of action potentials (nerve impulses) depends on 2 things

presence of myelin (salt vs continuous) & axon diameter

Axon Diameter

Larger = faster (less resistance)

Endoneurium

wraps around individual axons

Perineurium

wraps around fascicles (groups of axons), supports blood vessels

Epineurium

bundles fascicles together, encloses entire nerve to provide support & protection

How many layers of the cranial meninges? 3 layers

Pia Mater

innermost, high vascular layer (pia, arachnoid, dura)

Pia Mater

thin & delicate layers that closely follow contours of brain (pia, arachnoid, dura)

Arachnoid Mater

composed of a delicate web of collagen & elastic fibers (pia, arachnoid, dura)

Arachnoid Mater

supports arteries & veins in subarachnoid space (pia, arachnoid, dura)

Dura Mater

external, tough, dense irregular connective tissue (pia, arachnoid, dura)

Cerebral Spinal Fluid

clear, colorless liquid produced by ependymal cells, surrounds CNS & circulates in ventricles & central canal

What are the 3 functions of CSF?

buoyancy, protection, & environmental stability

Buoyancy

brain floats in CSF (reduce weight by 95%), preventing brain from being crushed by itself or sinking through foramen magnum

Protection

liquid cushion to protect delicate structures from striking cranium during sudden & forceful movements (“movement buffer”)

Environmental Stability

transports nutrients to the brain, removes waste, & prevents chemical fluctuations that would disrupt neuron function

Cerebrum

location of conscious thought process, origin of all complex intellectual functions, center of your intelligence, reasoning, sensory perception, thought, memory, judgement, voluntary motor, visual, & auditory activities (enables

Cerebral Hemispheres

2 halves (right & left)

Diencephalon

contains thalamus, hypothalamus, epithalamus (pineal gland), relay and switching centers for some sensory and motor pathways, controls visceral activities

Thalamus

sensory impulses from all the conscious senses (except olfaction) converge and get projected to correct area, filters information to allow only small portion of sensory info to reach cerebrum, “clues in” cerebrum where sensory info came from

Hypothalamus

controls autonomic nervous system to maintain homeostasis, influences HR, BP, respiration, food intake, water intake, body temp, emotional behavior, & sleep cycle, controls endocrine system

Pineal Gland

endocrine gland controlled by hypothalamus, secretes the hormone melatonin (circadian rhythm)

Brainstem

3 regions (midbrain, pons, medulla oblongata), bidirectional passageway for all tracts going between the cerebrum and the spinal cord, contains autonomic and reflex centers required for survival

Midbrain

short, superior segment, visual reflex centers & auditory reflex centers

Pons

broad, anterior bulge, inferior to midbrain, houses the pontine respiratory center- regulates skeletal muscles for breathing

Medulla Oblongata

continuous with spinal cord, regulates autonomic functions vital for life, cardiac center (HR), vasomotor center (BP), medullary respiratory center, other reflexive action (coughing, sneezing, etc.)

Cerebellum

posterior aspect, inferior to cerebrum (2nd largest region), outer surface is gray matter, deeper surface is white matter (arbor vitae), fine-tunes skeletal muscle movement & ensures contractions are smooth & coordinated, adjusts skeletal muscle to maintain equilibrium & posture, sends info to cerebrum so consciously aware of body position, stores memories of learned movement patterns

Arbor Vitae

branching, fernlike pattern

Corpus Callosum Function

tracts that allow communication between hemispheres, communicates with opposite side of body (100s of millions of myelinated axons)

Gyri

thick folds that increase surface area

Sulci

shallow depressions that house blood vessels

Frontal Lobe Function

voluntary motor functions, concentration, decision making, planning, personality, verbal communication