Benchmark exam II

what does the nervous system

-perception and experience of world

-voluntary movement

-consciousness, personality, learning, and memory

what aspects of homeostasis is regulated with the nervous system

-respiratory rate

- BP

-body temp

-sleep/wake cycle

-blood pH

what are the two anatomical divisions of the Nervous System?

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

What are the functional divisions of the nervous system?

Sensory (afferent) Division (towards)

Motor (efferent) Division (away)

Integrative functions

what is the sensory (afferent) division of the Nervous system?

part of the PNS: 2 subdivisions

Somatic Sensory Division (special sensory division)

Visceral Sensory division

gathers information about internal and external environments

input from the 2 subdivisions carried from receptors to spinal cord or brain by spinal and cranial nerves

what is the somatic sensory division? (subdivision of afferent division)

special sensory division

carries signals from skeletal muscles, bones, joints, and skin

• -organs for vision, hearing, taste, smell, and balance

what is the visceral sensory division? (subdivision of afferent division)

transmits signals from viscera

• -heart, lungs, stomach, kidneys, and urinary bladder

what are the integrative functions of the nervous system?

analyze and interpret incoming sensory information and determine response

• -99% of information subconsciously disregarded as unimportant

• -remaining stimuli leads to motor response

what is the motor (efferent) division of the nervous system?

actions performed in response to integration by PNS: by organs that neurons contact

• -motor neurons

• -effectors

2 subdivisions

Somatic (voluntary)

Autonomic (involuntary)

what are motor neurons?

carry out motor functions

travel from brain and spinal cord via cranial and spinal nerves

what are effectors?

organs that carry out effects of nervous system

what is the somatic motor division? (subdivision of efferent division)

neurons transmit signals to skeletal muscles (voluntary control) voluntary motor division

what is the autonomic nervous system (ANS; visceral motor division) (subdivision of efferent division)

neurons carry signals to thoracic and abdominal viscera, homeostasis

regulates secretion of glands, contraction of cardiac muscle

involuntary (involuntary motor division)

what are neurons?

excitable cells- sending and receiving signals as APs

consist of three parts

• -cell body (soma)

• -Dendrites

• -Axon

what is the cell body of a neuron?

most metabolically active

manufactures proteins needed for neuron

support high level of biosynthetic activity

what is the dendrite of a neuron?

short, branched processes

receive input from other neurons- transmit toward cell body as electrical impulses

multiple dendrites

what is the axon of a neuron?

only one axon (nerve fiber)

generate and conduct APs

distinct regions of axon:

• -axon hillock

• -axon collaterals

• -axon terminals (synaptic bulbs)

• -axolemma

what is the axon hillock of an axon?

where axon originates from cell body

what are the axon collaterals of an axon?

branches extending from main axon

what are the axon terminals (synaptic bulbs) of an axon?

arise from telodendria

components that communicate with target cell

what is the axolemma of the axon?

plasma membrane surrounding axon and its cytoplasm (axoplasm)

how do substances travel through axoplasm?

slow axonal transport

fast axonal transport

what is slow axonal transport?

transport substances (cytoskeleton proteins) from cell body through axon

rate of 1-3 mm/day

what is fast axonal transport?

requires motor proteins and consumes ATP

vesicles and membrane-bound organelles travel back toward (retrograde) or away (anterograde) cell body

rate of 200 mm/day and 400mm/day respectively

nervous tissue

neuron structure

what are the 3 functional regions of a neuron?

Receptive region- dendrites and cell body

conducting region- axon

secretory region- axon terminal

what are the three functional groups of a neuron?

-Sensory (afferent) neurons

-Interneurons (association) neurons

-motor (efferent) neurons

what are sensory (afferent) neurons?

carry information toward CNS

cell bodies in PNS receive information from sensory receptors and relay information via axons

pseudo unipolar or bipolar

what are interneurons (association neurons)?

relay information within CNS between sensory and motor neurons in body

multipolar

communicate with many other neurons

what are motor (efferent) neurons?

carry information away from cell body in CNS to muscles and glands

multipolar

what are multipolar neurons?

single axon and multiple dendrites: highly branched dendritic tree

motor. interneurons

found mostly in CNS, motor neurons in PNS

what are bipolar neurons?

one axon and one dendrite

sensory (afferent) neurons

found in special sense organs in PNS (retina and olfactory epithelium)

what are pseudo unipolar neurons?

single short process that splits into two axons (no dendrites); one fused axon divides into tow processes: one carries sensory information from sensory receptors to cell body

sensory (afferent) neurons

found in sensory neurons in the PNS associated with touch, pain, and vibration sensations

what are the neuron components in the CNS?

nuclei- clusters of neuron cell bodies

tracts- bundles of axons

what are the neuron components in the PNS?

Ganglia- clusters of neuron cell bodies

nerves- bundles of axons

what are neuroglia (neuroglial) cells?

provide structure support and protection for neurons

maintain their environment

4 types in CNS:

• -astrocytes

• -oligodendrocytes

• -microglia

• -ependymal cells

2 types in PNS:

• -Schwann cells

• -satellite cells

what are astrocytes?

anchor, transport, BBB

in CNS

what are oligodendrocytes?

myelin in CNS

what are microglia?

phagocytosis (recycling material and immune function)

what are ependymal cells?

CSF in CNS

what are Schwann cells?

myelin in PNS

what are satellite cells?

surround and protect

what is myelin Sheath?

layers of plasma membrane of Schwann cell (PNS) or oligodendrocyte (CNS)

what is myelination?

neuroglial cells wrap multiple layers of membrane (myelin) around axon

• -lipid content insulates axon (prevent ion movement) increases speed of AP conduction

• -myelinated axons conduct AP about 15- 20 times faster

what are nodes of Ranvier?

gaps between adjacent neuroglia; myeline sheath is absent

Myelin Sheath

what is the typical myelination of small axons in the CNS and PNS?

they are usually unmyelinated

what is white matter?

myelinated axons; appear white

what is gray matter?

composed of neuron cell bodies, unmyelinated dendrites and axons

appear gray

what is regeneration?

replacement of damaged tissue

where does regeneration occur and when can regeneration occur?

nonexistent in CNS and limited in PNS

can only regenerate if cell body remains intact

what breaks down after an axon is injured?

the axon and myelin sheath break down distal to injury (Wallerian Degeneration), helped by phagocytes

where do new growth processes start?

from the proximal end of the axon

what forms the regeneration tube?

Schwann cells and basal lamina

what guides the new axon to its target?

a single growth process growing into the regeneration tube

what happens when the new axon reaches its target?

it reconnects to the target cell

what type of stimuli can excite a neuron?

chemical signals, local electrical signals, and mechanical deformation

what do stimuli generate in neurons?

electrical changes across the neuron plasma membrane

how are electrical changes in neurons conducted?

they are rapidly conducted along the entire length of the membrane (conductivity)

what is the typical resting membrane potential (RMP) of a neuron?

-70 mV

what two forms of electrical changes occur in neurons?

Local potentials- travel short distances

action potentials- travel entire length of axon

what are local potentials (graded potentials)

small local changes in potential of neuron’s plasma membrane; triggers for long-distance APs

cause one of 2:

depolarization

hyperpolarization

what is depolarization?

positive charges enter cytosol; make membrane potential less negative (-70 to -60)

what is hyperpolarization?

either positive charges exit or negative charges enter cytosol; makes membrane potential more negative (-70 to -80)

what are local anesthetics?

lidocaine

administered for surgical or dental procedures; produce temporary numbness in specific areas

how do local anesthetics work?

block voltage-gated sodium channels in treated areas; prohibits depolarization; APs relaying pain do not go to CNS

nonselective; also affect sodium channels in muscles- temporary paralysis of muscles

what is the all-or-none principle?

refers to event that either happens completely or not at all

what is the refractory period?

period after neuron has generated AP; cannot be stimulated to generate another AP

2 phases:

absolute refractory period

relative refractory period

what is conduction speed?

rate of propagation; influenced by both axon diameter and myelination; determines how rapidly signaling can occur with nervous system

larger diameter- faster conduction-lower resistance

two types of conduction:

• -saltatory

• -continuous

what is saltatory conduction?

myelinated axons increase efficiency and speed of signal conduction; APs only depolarize nodes of Ranvier; jumps from node to node

what is continuous conduction?

unmyelinated axons; every section of axolemma from trigger zone to axon terminal must propagate AP; slows conduction speed as each section of axon must depolarize

what are type A fibers?

fastest conduction speed (120m/sec) largest diameter (5-20) and myelinated

sensory and motor axons- skeletal muscle and joints

what is type B fibers?

slower conduction speeds (15m/sec) mostly myelinated with intermediate diameter axons (2-3)

efferent fibers of ANS and sensory axons

what is type C fibers?

slowest (.5-2m/sec) smallest diameter (.5-1.5) unmyelinated axons

efferent fibers of ANS and sensory axons

pain, temp, pressure sensations

what is multiple sclerosis (MS)

certain cells of immune system attack myelin sheaths with CNS

autoimmune disorder

progressive loss of myelin sheath; loss of current from neurons

what are the symptoms of MS?

changes in sensation (numbness), alterations in behavior and cognitive abilities, and motor dysfunction, including paralysis

what are synapse?

where neuron meets target cell (neuronal synapse if another neuron) can be electrical or chemical

what is presynaptic neuron?

neuron sending message from its axon terminals

what is postsynaptic neuron?

neuron receiving message from presynaptic neuron at its cell body, axon, or dendrites

what are electrical synapse?

occurs between electrically coupled via gap junctions

how are cells physically arranged at synapses to allow communication through gap junctions?

the axolemmas of each cell are nearly touching and gap junctions align channels to form pores that allow ions or other small substances to flow through

in what type of brain areas are electrical synapses commonly found?

they are found in areas of the brain responsible for automatic behaviors like breathing

cardiac and visceral smooth muscle to allow for coordinated muscle activity

what are chemical synapses?

more efficient than electrical; no signal strength is lost

synaptic vesicles- transmit signals from presynaptic to postsynaptic neurons

synaptic cleft separate presynaptic and postsynaptic neurons

events at chemical synapse

1.Action potential in presynaptic neuron triggers opening of voltage-gated calcium ion channels in axon terminal

2.Influx of calcium ions causes synaptic vesicles to release neurotransmitter into synaptic cleft

3.Neurotransmitters bind to receptors on postsynaptic neuron

4.Ion channels open, leading to local potential and possibly action potential if threshold reached

what are postsynaptic potentials?

local potentials in membranes of postsynaptic neuron

what are excitatory postsynaptic potential (EPSP)

Membrane potential of postsynaptic neuron moves closer to threshold; caused by small local depolarization (sodium or calcium channels open)

what are inhibitory postsynaptic potential (IPSP)

Membrane potential of postsynaptic neuron moves farther away from threshold; caused by small local hyperpolarization (potassium or chloride ion channels open)

what is neural integration?

process in which postsynaptic neuron integrates all incoming information into single effect

what is summation?

all input from several postsynaptic potentials are added together (EPSPs + IPSPs) to affect membrane potential at trigger zone

types of summation:

• -temporal summation

• -spatial summation

what is temporal summation?

NT releases repeatedly from axon terminal of single presynaptic neuron; each local potential (EPSP) is short-lived

must be generated quickly to reach threshold and create AP

what is spatial summation?

simultaneous release of NTs from axon terminals of many presynaptic neurons

what are venomous arthropods?

spiders, and scorpions, many venoms affect neuronal synapses- neurotoxins

what do female black widows cause?

toxin causes massive release of NT, repetitive stimulation of postsynaptic neuron

what do bark scorpion cause?

most lethal of 40 species; prevents postsynaptic sodium channels from closing, membrane remains polarized, continues to fire APs

what are common symptoms of venom?

muscle hyperexcitability, sweating, nausea and vomiting, and difficulty breathing

what is treatment and prognosis for venom?

depends on amount and availability of medical care; severe cases usually require antivenin

what is acetylcholine (ACh)?

small molecule NT widely used by nervous system

cholinergic synapses bind ACh

largely excitatory; some inhibitory in PNS

synthesized from choline and acetyl-CoA- packed in synaptic vesicles

degraded by AChE

what is biogenic amines? (monoamines)

5 NTs synthesized from amino acids used CNS and PNS for regulation of homeostasis

first 3 form catecholamine subgroups (tyrosine)

excitatory

what is Norepinephrine? (biogenic)

catecholamine; noradrenalin

mainly in ANS influences HR, BP, and digestion

in CNS sleep/wake cycle, attention, and feeding