APK2100C Ch 12

What does the nervous system do?

Control and communicate with other systems of the body

What do NS signals do

Cause immediate responses by body (specific and rapid)

NS basic function

relay info about environment (aka stimuli) and then initiate response

What are the three overlapping functions of the nervous system?

1)Sensory input 2) Integration 3) Motor Output

Sensory recptors

Monitor changes inside and outside of the body (internal or external) send that info to CNS

Integration

CNS receives and interprets sensory input and makes action decision (aka association– triggers output)

Motor Output

Motor neurons elicits responses by activating effector organs

Divisions of NS

CNS vs PNS

What’s the CNS?

Brain and Spinal Cord ONLY

What’s the CNS functions?

integration and command (association)

What’s the PNS?

nerves and ganglia

Ganglia

groups of neurons outside of the brain and Sp Cord

What does the PNS do?

communicate from CNS to/ from effector organs

Portions of PNS

Sensory division and Motor Division

What are the parts of the Sensory division

Somatic and visceral

What are the parts of the Motor Division?

Somatic and Viscera

What’s another term associated with sensory?

afferent (arriving at CNS)

WHat’s another term associated with Motor?

efferent (Exit CNS

What part of the body deals with somatic?

outside of ventral body cavity, aka not guts

What parts of the body are visceral?

ventral boy cavity

What does the somatic motor division control?

skeletal muscles, voluntary action

What does the visceral motor division control?

involuntary actions (smooth musc and cardiac)

Types of Nervous Tissue

Neurons and Neuroglia (support cells)

Special Characteristics of Neurons

1) Conduction 2) Longevity 3)Not able to Divide 4)High Metabolic Rate

Conduction

Sends electrical signals from one body part to another (aka action potentials/ nerve impulses)

Longevity

Neurons last a lifetime (few PNS exceptions)

How are neurons removed?

via neural pruning

Not able to divide

Neurons can’t replace themselves

Most common type of brain tumor

Giloma. The glial cells are able to divide and one of few types of NS tissue that can accumulate errors in DNA

High metabolic Rate

require constant supply of O2 and nutrients

Parts of Neuron

dendrites, soma, axon, terminal bouton, axon hillock

Dendrites

Receive info from other neurons

Soma

Cell body, with organelles

Axon hillock

part of soma that conducts the signal to start an AP down the axon

Initial segment of axon

start AP, acts as gate (non-myelinated?)

Axon

can vary in size, sends out the AP and ends at terminal bouton often wrapped with myelin sheaths to better conduct the signals

Terminal Bouton

creates synapses with other neurons’ dendrites Have enlargement at the ends of it, axon terminal

Tracts

axons that travel together, esp in CNS

Structural Classifications of Neurons

Multipolar, unipolar, and bipolar

Multipolar

many processes extend from cell body, all are dendrites except for single axon

bipolar

2 processes extend from cell body, one fused dendrite and one axon

Unipolar

aka pseudo polar one process extends from cell body and forms central and peripheral processes, together are an axon

What is unipolar called pseudo polar?

because usually are result of fused together, used to be bipolar

Peripheral process

part of unipolar process that works similar to dendrite axons

Central process

part of unipolar process that functions like an axon

What are unipolar neurons usually used as

Sensory

Functional classification of Neurons

grouped according to direction of nerve impulse traveling relative to CNS Afferent, efferent and interneurons

Afferent

towards CNS= SENSORY neurons

Efferent

away from CNS= MOTOR neurons

Interneurons

within CNS= ASSOCIATION neurons

synapses

connect both Neuron to neuron and neuron to effector organ

Types of effector organs

muscles nd glands

What type of neurons make up a synapse?

presynaptic neuron and postsynaptic neuron

Synaptic cleft

the space between the connecting parts of a synapse where neurotransmitters pass through to the postsynaptic neuron

3 areas of possible connection

1) axosomatic (on cell body) 2) axodendritic 3)axoaxonic (rare)

How are neurotransmitters transported?

in the axon they are carried via synaptic vesicles (made from plasma membrane) travel freely through synaptic cleft (until picked up again)

Are there mitochondria in the axon terminals?

yes, energy needed for exocytosis (though might not be in very ends of it)

Types of CNS Neuroglia

-Astrocytes -Microglia -Ependymal cells -Oligodendricytes

2 types PNS neuroglia

satellite cells schwann cells

Astrocytes

-most abundant CNS neuroglia -form BBB on capillaries -lots of processes (one soma)

Microglial cells

smallest glial cell -similar to WBC -looks for debris and phagocytos or send to blood

Ependymal cells

line cavities -Don’t make CSF but excrete it -Cilia that moves CSF -Type of epithelial tissue? support function

Oligodendrocytes

processes that form myelin sheathes around CNS axons End foot can wrap around multiple axons

Are there nerves in the brain or spinal cord?

NO WAY, only in PNS

Satellite cells

covers neuronal soma in PNS

Schwann Cells

form myelin sheaths in PNS, only covers one axon, gets squished up middle part

Schwann vs oligodendricyte

SCH- covers only ONE axon and in PNS OLIG- Covers multi axons and in CNS both are myelin sheaths

What are the spaces between myelin sheaths?

nodes of Ranvier (input lots of sodium and potassium, continue the AP)

Myelin

mlitlayered lipoprotein structure that wraps pieces of axons

Functions of myelin

-electrical insulate axon -speeds rate of AP conduction

examples of myelin cells

Schwann cells PNS oligodendricytes CNS

Nodes of Ranvier

gaps in myelin sheath

Neurilemma

outer, nucleated, cytoplasmic layer of schwann cells, outermost layer of myelin sheath. (squished part) ONLY in PNS.

What makes up the walls of an axon?

plasma membrane, there’s stuff inside too!

Where does regeneration of myelin sheaths start?

In neurilemma

How is neurilemma formed?

from the tight wrapping of the glial cell around the axon, pushes organelles and cytoplasm to the side

Why is there neurilemma?

when there’s damage, it forms a regeneration tube, tunnel that connects one end of a damaged axon to another end (send out chemical to guide growth)

Where is a regeneration tube found?

ONLY in PNS, no neurilemma in CNS

Where is white matter in the brain?

inner parts, surrounded by grey matter

Where is white matter in spinal cord?

outer layer, surrounds gray matter

Ganglion

cluster of soma in PNS

Nucleus

cluster of soma in CNS (part of gray matter)

Nerve

groups of axons in PNS

Tract

cluster of axons in CNS (looks like white matter b/c of myelin)

Nerves

-cable like organ in PNS – parallel axons in bundles aka fascicles -each axon within is covered in Schwann cell (both myelinated and not)

Unmyelinated neurons in PNS

can still have 1 layer of schwann cell wrapped around and still be unmyelinated

CT in the PNS

endoneurium, perineurium, and epineurium

Endoneurium

surrounds schawann cells

perineurium

surrounds fascicles

Epineurium

surrounds entire nerve (including some blood vessels)

Reflex

rapid, automatic motor responses to stimuli

Reflex arc

simple chair of neurons that cause reflexes (non cognitive, automatic response)

Components of reflexes

1) receptors 2) sensory neuron 3) integration center 4)motor neuron 5) effector

Monosynaptic reflexes

no interneuron, one synapse, super fast often stretch reflex

Polysynaptic reflexes

multiples interneurons, multiple synapses, often withdrawal reflex (pain)

The simplest type of reflex, in which there is no interneuron between the sensory and motor neuron, is called a ________ reflex.

monosynaptic

Nerve fascicles are bound into bundles by a wrapping of connective tissue called ________.

perineurium

The basic components of the peripheral nervous system are ______ and ______.

CN and Spinal nerves

Where is the structural link between the CNS and PNS located?

Only in the cerebral cortex In the gray matter of the CNS In sensory neurons in the dorsal root and dorsal root ganglia In motor neurons in the ventral root of the spinal nerve

What important function could be diminished if the cilia on ependymal cells were absent?

circulation of CSF

The peripheral process and central process of a sensory neuron together are both part of the ________.

Axon

Within the white matter of the CNS, axons traveling to similar destinations are bundled together in ________.

tracts

_____ neurons are rare neurons, but are located in the retina and in the olfactory mucosa.

bipolar

Which of the following sequences puts the components of a reflex arc in the correct order of their activation?

Receptor, sensory neuron, integration center, motor neuron, effector