BIO 3200: Chapter 9

What are the components of the central nervous system?

brain and spinal cord

What are the components of the peripheral nervous system?

sensory (afferent) neurons and efferent neurons

Which PNS glial cell supports cell bodies?

satelite cells

What is a basic reflex pattern in the nervous system?

stimulus → sensor → input signal → integrating center → output signal → target → response

The Peripheral Nervous System divides into what two divisions?

Sensory division and Efferent division

Sensory division of the PNS

sends information to the CNS through afferent (sensory) neurons

Efferent division of the PNS

takes information from the CNS and outputs them as efferent neurons

What are the two pathways of the sensory division of PNS?

afferent signal pathway and enteric system pathway

Steps of the Afferent signal pathway

1) signal

2) sensory receptor

3) sensory neurons (afferents)

4) integrates in CNS

Steps of the enteric system pathway

1) signal

2) neurons of enteric system

3) sensory neurons (afferent)

4) integrates in CNS

_______ ______ continuously monitors conditions in the internal and external environments in the PNS.

sensory receptors (afferents)

Efferent neurons are subdivided into two categories:

somatic motor division and autonomic division

Somatic motor division

controls skeletal muscle

Autonomic division

controls smooth/cardiac muscles, exocrine glands, some endocrine glands, and some adipose tissues

Autonomic division (visceral nervous system)

controls contraction and secretion in various internal organs (viscera)

Autonomic neurons can be divided into 2 branches:

sympathetic (fight or flight) and parasympathetic (rest and digest)

Basic pathway for efferent division

1) CNS sends response based on info from afferents

2) response sent to efferent neurons

3) autonomic neurons activate and has several paths to choose from

4) the appropriate branch is activated based on info

5) tisue response

6) sends feedback to sensory receptors (afferents)

Enteric Nervous System

network of neurons in the walls of the digestive tract

Which division of the PNS controls the enteric nervous system?

the autonomic division, but also is able to function autonomously as its own integration center

TRUE OR FALSE: can the CNS initiate activity w/o sensory input

TRUE - like when u decide to text a friend out of the blue

TRUE OR FALSE: the CNS needs to create an output to the efferent divisions

FALSE: u do NOT need any measurable output, think of thinking or dreaming

What are the two cell types making up the nervous system?

neurons and glial cells

Neurons

the basic signaling units of the nervous system

Glial cells

supporting cells of the nervous system

Which cell is known as the functional unit of the nervous system?

neuron

What is the function of Dendrites?

receive incoming signals, or axons

What are the two essential features that allows neurons to communicate with one another?

axons and dendrites

Structurally, how are neurons classified?

by the number of processes that originate from the cell body

Anaxonic neurons lack what?

an identifiable axon but have numerous dendrites

Where are bipolar neurons found?

the olfactory epithelium and retina of the eye

What is the function of sensory neurons?

to carry information about temperature, pressure, light, and other stimuli from sensory receptors to the CNS

What type of neuron is a peripheral sensory neuron?

pseudounipolar- cell bodies located close to the CNS and very long processes extend out to receptors in the limbs and organs

Function of efferent neurons

both somatic and autonomic neurons carry output signs from the CNS to target cells

Structure of nerves

long axons of all peripheral neurons are bundled together with connective tissue fibers

In which direction do nerves extend from the CNS?

outward

Nerves that only carry efferent signals are

motor nerves

Nerves that carry signals in both directions are

mixed nerves

Interneurons

neurons that lie entirely within the cns

Cell body (soma) function

contains DNA that is the template for protein synthesis

mRNA made in this structure is transported to distant parts of the neuron to direct local protein synthesis

Which structure increases the surface area of a neuron?

dendrites

What is the primary function of dendrites in the PNS?

to receive incoming information and transfer that info to an integrating region within the neuron.

What is the primary function of an axon?

to transmit outgoing electrical signals from the integrating center of the neuron to target cells at the end of the axon

Why do axons divide into branching?

it allows a single neuron to communicate with multiple target cells

Where is the trigger zone found on an axon?

axon hillock, its where the axon joins the cell body

Where are neurotransmitters released into the synapse?

axon terminal- distal end of the neuron

What do axon terminals contain?

mitochondria for atp production, mRNA for protein synthesis, proteasomes for local protein degradation, and membrane-bound vesicles filled with neurocrine signal molecules

What structures stores and releases neurotransmitters?

axon terminals and varicosities

Where do neurohormone-secreting neurons terminate?

close to blood vessels so that neurohormones can enter circulation

What is the difference betwen a nerve and neuron?

a neuron is a single nerve cell

a nerve is a bundle of axons from many neurons

Axonal transport

movement of material between the axon terminal and the cell body

Forward (anterograde) transport

moves vesicles and mitochondria from the cell body to the axon terminal

Backward (retrograde) transport

returns old cellular components from the axon terminal to the cell body for recycling

What helps cargo move in axonal transport?

the motor proteins (kinesin and dynein) alternately bind and unbind to the microtubules with the help of ATP

Fast axonal transport

goes in both directions and can move vesicles/membranous organelles at rates of 400mm

Slow axonal transport

moves soluble proteins and cytoskeletal proteins from the cell body to the axon terminal at a rate of 0.2-10 mm/day.

What can slow transport only be used for?

components that are not consumed rapidly by the cell

ex) cytoskeleton proteins

Steps of fast axonal transport

1) walks vesicles/mitochondria along microtuble network

2) the axon terminal has mitochondria and numerous vesicles

3) old organelles are recycled back to the cell body

4) retrograde fast axonal transport

5) old membrane components digested in lysosomes

Which mutations or alterations in proteins associated with axonal transport have been linked to a variety of inherited disorders?

microcephaly ( small head ) and fragile X syndrome, alzheimers

Synapse

the region where an axon terminal meets its target cell

The neuron that delivers a signal to the synapse is known as

the presynaptic cell

The cell that receives the signal from the synapse is known as

the postsynaptic cell

The synaptic cleft

the narrow space between two c3lls

What is the synaptic cleft filled with?

extracellular matric and adhesion molecules (cahedrins)

What holds the presynaptic and post synaptic cells in position?

cahedrins

The vast majority of synapses in the body are

chemical synapses

Chemical synapses

where the presynaptic cell releases a chemical signal that diffuses across the synaptic cleft and binds to a membrane receptor on the post synaptic cell

Electrical synapses

where electrical signals pass directly from cell to cell through gap junctions

The axons of embryonic nerve cells send out special tips called ____ _____ that extend through the extracellular compartment until they find their target cell.

growth cones

What signals do growth cones depend on to find their way?

growth factors, molecules in the ECF matrix, and membrane proteins on the growth cones.

Once an axon reaches its target cell, a _________ forms.

synapse

What prevents a synapse from disappearing?

synapse formation must be followed by electrical and chemical activity

Neurotrophic factors

chemicals secreted by Schwann cells that keep damaged neurons alive

What is brain growth dependent on?

an increase in size/number of axons, dendrites, and synapses

Why do babies who are neglected or deprived of sensory input experience delayed development?

lack of nervous system stimulation

The PNS has two types of glial cells, what are they?

schwann cells and satelite cells

The CNS has four types of glial cells, what are they?

oligodendrocytes, astrocytes, microglia, and ependymal cells

Primary function of glial cells

physical support and communication with neurons/provide critical biochemical and structural support

Which glial cells support and insulate axons by forming myelin?

Schwann cells (PNS) and oligodendrocytes (CNS)

Myelin

a substance composed of multiple concentric layers of phospholipid membrane

What does myelin do other than provide physical support?

act as insulation around axons and speeds up their signal transmission

Which glial cell is a nonmyleniating cell?

satelite cell

Satelite cell function

form supportive capsules around nerve cell bodies located in ganglia

Ganglion

a collection of nerve cell bodies found outside the CNS

Astrocytes

highly branched CNS glial cells that make up half of all cells in the brain

take up: K⁺, water, and neurotransmitters

secrete: neurotrophic factors

help form: blood-brain barrier

provide: substrates for ATP production

Primary role of astrocytes

maintain homeostasis in the brain

Microglia

immune cells that reside permanently in the CNS

scavenger cells

Ependymal cells

cells that form a selectively permeable epithelial layer (ependyma) separates the fluid compartments of the CNS

What is the one source of neural stem cells?

ependyma

Excitable tissues

ability to propagate electrical signals rapidly in response to a stimulus

ex) nerve and muscle cells

Na⁺, Cl^-, and Ca²⁺ are more concentrated in the _____ _____ _____.

extracellular fluid

Potassium K⁺ is more concentrated in the __________.

cytosol

The resting membrane potential is much more permeable to what molecule?

Potassium K⁺

Why is the resting membrane potential -70 V_m?

At rest, the neuron is much more permeable to K⁺ because it has many K⁺ leak channels, allowing K⁺ to leave the cell and helping make the inside negative

What are the two factors influence the membrane potential?

the uneven distribution of ions across the cell membrane, and differeing membrane permeability to those ions

The nernst equation

calculates the equilibrium potential of one ion and accounts for its concentration gradient and electrical charge.

Goldman-Hodgkin-Katz equation

calculates the membrane potential that results from the contribution of all ions that can cross the membrane.

The _____ _______ is the primary site where a neuron integrates incoming signals and determines whether to fire an action potential.

trigger zone

Equillibrium Potential

the membrane potential at which there is no net movement of a specific ion across the membrane.