GVSU BMS 250 TEST 3

Central Nervous System

brain and spinal cord

Peripheral Nervous System

cranial and spinal nerves

Sensory Nervous Sytem

detects stimuli and transmits info from receptors to the CNS. Somatic& Visceral

Afferent Division

Sensory nervous system

Somatic Sensory

sensory input that is consciously perceived from receptors (eyes, ears, and skin)

Visceral sensory

sensory input that is not consciously perceived from receptors of blood vessels and internal organs (ex. heart)

Motor Nervous System

initiates and transmits info from the CNS to effectors. Somatic& Autonomic

Efferent Division

Motor Nervous system

Somatic Motor

Motor output that is consciously or voluntarily controlled; effector is skeletal muscle

Autonomic Motor

Motor output that is not consciously or is involuntarily controlled; effectors are cardiac muscle, smooth muscle, and glands

General Characteristics of Neurons

excitability, conductivity, secretion, extreme longevity, and amitotic

Excitability

responsiveness to a stimulus. stimulus causes change in cell's membrane potential

Conductivity

ability to propagate electrical signal. voltage gated channels along membrane open sequentially

Secretion

release of neurotransmitters in response to conductive activity. messenger is released from vesicle to influence target cell

Extreme Longevity

cell can live throughout person's lifetime

Amitotic

after fetal development, mitotic activity is lost in most neurons

Parts of a neuron

cell body (soma), dendrites, axon

Cell Body (Soma)

Plasma membrane encloses cytoplasm. contains nucleus. initiates some graded potentials, receives others from dendrites; conducts these potentials to axon

Dendrites

short, unmyelinated processes branching off cell body. receive input and transfer it to cell body

Axon

long process emanating from cell body. makes contact with other neurons, muscle cells, or glands. Attaches to cell body at axon hillock. cytoplasm called axoplasm; membrane called axolemma. ends in several telodendria(axon terminals). tips of telodendria are synaptic knobs. synaptic knobs house synaptic vesicles containing neurotransmitter. axons function to conduct action potentials and then releases neurotransmitter at synaptic knob

Neuron Transport

axons move material to and from the cell body. Anterograde, retrograde, fast axonal, and slow axonal transport

Anterograde Transport

from cell body. moves newly synthesized material toward synaptic knobs

Retrograde Transport

to cell body. moves used materials from axon for breakdown and recycling some

Fast Axonal transport

occurs about 44o mm per day. involves movement across microtubules. powered by motor proteins that split ATP. Anterograde (transport of vesicles, organelles, glycoproteins) or Retrograde(transport of used vesicles, potentially harmful agents) motion possible

Slow Axon Transport

occurs at about 0.1 to 3 mm per day. results from flow of axoplasm. substances only moved from cell body toward knob (enzymes, cytoskeletal components, new axoplasm)

Structural Classifications of Neurons

by number of processes coming off soma. multipolar, bipolar, unipolar, and anaxonic

Multipolar Neurons

many dendrite, one axon extend from soma. most common type

Bipolar Neurons

one dendrite and one soma extend from soma, limited number(ex. retina in eye)

Unipolar Neurons (pseudounipolar)

one axon extends from soma. axon splits into two processes (peripheral and central)

Peripheral Process

splits into several receptive dendrites

Central Process

leads to synaptic knobs in CNS

Anaxonic Neurons

have dendrites but no axons

Functional Classifications of Neurons

sensory, motor, interneurons

Sensory neurons (afferent)

conduct input from somatic and visceral receptors to CNS. most are unipolar( a few bipolar)

Motor Neurons (efferent)

conduct output from CNS to somatic and visceral effectors. all are multipolar

Interneurons (association neurons)

receive, process, and integrate info from many other neurons. communicate bt sensory and motor neurons. located within CNS; make up 99% of our neurons. generally are multipolar.

Nerve

a bundle of parallel axons in the PNS. wrapped in connective tissue wrappings (epineurium, perineurium, and endoneurium)

Epineurium

encloses entire nerve. thick layer of dense irregular connective tissue

Perinerium

wraps fascicle (small bundle of axons in nerve). layer of dense irregular connective tissue

Endoneurium

wraps an individual axon. delicate layer of areolar connective tissue. separates and electrically insulates each axon

Cranial nerves

extend from brain

Spinal Nerves

extend from spinal cord

sensory nerves

contain sensory neurons sending signals to CNS

Motor nerves

contain motor neurons sending signals from CNS

Mixed Nerves

contain both sensory and motor neurons. most named nerves are in this category. individual axons in these nerves transmit only one type of info

Synapse

place where a neuron connects to another neuron or an effector. chemical and electrical

Electrical Synapse

presynaptic and post synaptic neurons bout together by gap junctions. fast: no synaptic delay in passing electrical signal

Chemical Synapse

far more common. Presynaptic neuron's axon terminal produces signal. post synaptic neuron receives signal. synaptic cleft.

Synaptic cleft

small fluid-filled gap between the two neurons

Events of synaptic communication

1. Neurotransmitter molecules released from vesicles of synaptic knob into cleft.

2. Transmitter diffuses across cleft and binds to postsynaptic receptors

3. Binding of neurotransmitter to receptor initiates postsynaptic potential (a graded potential). Synaptic delay: takes time for all these events

Glial Cells (neuroglia)

-nonexcitable, support cells found in CNS&PNS

-smaller, but far outnumber neurons (1/2 volume of nervous system)

-capable of mitosis

-protect and nourish neurons

-provide physical scaffolding for nervous tissue( guide migrating neurons during development)

-critical for normal function at neural synapses

Neuroglia of CNS

Astrocytes, Ependymal cells, Microglia, Oligodendrocytes

Astrocytes

-star shaped cells

-most abundant glial cells

-helps form the blood- brain barrier

-regulates interstitial fluid composition

-provides structural support and organization to CNS

-Assists with neuronal development

-replicates to occupy space of dying neurons

Ependymal Cells

-lines ventricles of brain and central canal of spinal cord

-assists in production and circulation of CSF

-ciliated simple cuboidal or simple columnar epithelial cells

Microglia

-phagocytic cells that move through the CNS

-protects the CNS by engulfing infectious agents and other potential harmful substances

Oligodendrocytes

-myelinates and insulates CNS axons

-allows faster action potential propagation along axons in the CNS

Neuroglia of PNS

Satellite cells & Neurolemmocytes

Satellite Cells

-arranged around neuronal cell bodies in a ganglion

-electrically insulates and regulates the exchange of nutrients and wastes

Neurolemmocyte (Schwann cells)

-elongated, flat cells that myelinated and insulates the PNS axons

-allows for faster action potential propagation along an axon in the PNS

Myelination

the process of wrapping an axon with myelin

Myelin

several layers of membrane of glial cells. high lipid content gives it glossy-white appearance and insulates axon. neurolemmocytes in PNS and oligodendrocytes in CNS

Multiple Sclerosis

-progressive demyelination of neurons in CNS

-autoimmune: oligodendrocytes are attacked by immune cells

-repeat inflammation causes scaring and permanent loss of function

Gullian- Barre syndrome

-loss of myelin from peripheral nerves due to inflammation

-muscle weakness but most function recovered w medical help

Axon Regeneration (PNS)

Regeneration possible if neuron cell body is intact and enough neurilemma remains. more successful is less damage and if distance between site of damage and structure is shorter

Neurilemma

formed from neurolemmocyte's cytoplasm and nucleus are pushed to periphery

Axon Regeneration (CNS)

-extremely limited

-oligodendrocytes secrete growth- inhibiting molecules; not growth factors

-large number of axons crowd CNS

-regrowth obstructed by scars from astrocytes and connective tissue

Pumps

-membrane proteins that maintain a concentration gradient by moving substances against their concentration gradient.

-require cellular energy

-neurons have sodium-potassium pumps and calcium pumps in their membranes

Channels

protein pores in the membrane that allow ions to move down their concentration gradients (in or out of the cell). leak, chemically gated, and voltage gated.

Leak (passive) Channels

always open for continuous diffusion

Chemically gated channels

normally closed, but open when neurotransmitter binds

Voltage gated channels

normally closed, but open when membrane charge changes.2 gates but 3 states(resting, activation,or inactivation)

Entire Plasma Membrane neuron has

leak channels (Na+& K+), Na+&K+ pumps, and maintain resting membrane potential

Receptive Segment (Dendrite and cell body)

chemically gated (Cl-) channels

Initial Segment (axon hillock)

voltage gated Na+ channels and voltage gated K+ channels

Conductive Segment (axon and branches)

voltage gated Na+ channels and voltage gated K+ channels

Transmissive Segment (synaptic knob)

voltage gated Ca2+ channels and Ca2+ pumps

Characteristics of resting neurons

-ions are unevenly distributed across the plasma membrane due to the actions of pumps (Higher concentration of K+ in cytosol and Na+, Cl-,Ca2+ in Interstitial fluid(IF))

-gated channels are closed in the functional segments of the cell

-there is an electrical charge difference across the membrane (cytosol is relatively negative, resting membrane potential is typically -70mV

Resting Membrane Potential

-K+ diffusion is the most important factor

-Since there are a few Na+ leak channels, Na+ also influences RMP

K+ diffusion

K+ diffuses out of the cell due to its concentration gradient, is limited by the electrical gradient(the pull of the negative RMP on the positive ion)

Graded potentials

it can vary in size