Functional Organization of Nervous Tissue Part 1

cells of nervous tissue

neurons and glial cells

neurons (3)

electrically excitable cells; receive process and transmit information

glial cells

supportive cells

Glial cells include

astrocytes, oligodendrocytes, microglia, ependymal cells

central nervous system cells

neurons
astrocytes
microglia
ependymal
oligodendrocytes

peripheral nervous system cells

neurons
satellite
schwann

microglia

innate immunity

astrocytes

maintain blood brain barrier, participate in synapses

ependymal

build barriers between compartments

Oligodendrocytes

produce myeline sheaths

satellite cells

support other cell bodies

schwann cells

produce myelin sheaths around axons

functions of the nervous system (5)

maintaining homeostasis
receiving sensory input
integrating information
controlling glands and muscles
establishing and maintain mental activity

divisions of the nervous system

central nervous system and peripheral nervous system

central nervous system (3)

- receives information from and sends information to the body

- decision maker

- consists of brain and spinal cord

peripheral nervous system (3)

- detects stimuli in and around the body

- carries info to the CNS and from CNS to body

- consists of nerves, ganglia, and sensory receptors

Structures of CNS

brain (housed in skull)
spinal cord (housed in vertebral column)

structures of the PNS

nerves, ganglia, sensory receptors

nerves are a

collection of axons outside the brain and spinal cord that can carry electrical signals to and from CNS

cranial nerves

12 pairs of nerves originating from the brain

spinal nerves

31 pairs of nerves originating from the spinal cord

plexus

bundle of nerves outside the brain and spinal cord

ganglia

group of neuron cell bodies outside the brain and spinal cord

sensory receptors

cells that respond to a specific stimuli

sensory receptors can be

neurons or specialized cells distributed throughout the body

divisions of PNS

sensory (afferent) division
motor (efferent) division

sensory (afferent) division

transmit electrical signals from receptors to the CNS

motor (efferent) division

transmits electrical signals from CNS to effector organs

effector organs

muscles (smooth, skeletal, cardiac) and glands

divisions of the motor nervous system (a branch of the PNS - efferent)

somatic and autonomic

somatic nervous system

voluntary division, regulates movement of skeletal muscles

autonomic nervous system

involuntary division, regulates contraction of cardiac and smooth muscle as well as gland secretion

divisions of the autonomic nervous system

sympathetic, parasympathetic, enteric nervous systems

sympathetic nervous system

- prepares the body for physical activity
- fight or flight

parasympathetic nervous system

- regulates resting functions (digesting food)
- rest and digest

enteric nervous system

neuronal networks in the wall of the digestive tract

Movement thru nervous system

sensory division of PNS detects stimuli and conducts action potential to CNS where it is interpreted. CNS then initiates action potential that is sent thru motor division of PNS (autonomic and somatic)

cells of nervous tissue

neurons and glial cells

neurons are

electrically excitable cells of the nervous system, around 100 billion neurons in the body

glial cells

supportive cells, 50% of brain's weight, 10-50x more glial cells than neurons in various brain regions

parts of a neuron

cell body, dendrites, axon

cell body of a neuron

- soma
- single, centrally located nucleus with the nucleolus

significant structures of the cell body

nissl bodies
neurofilaments (intermediate filaments)
microtubules

nissl bodies

extensive rough endoplasmic reticulum

in the cell body, there are also

abundant intermediate filaments (neurofilaments) and microtubles forming bundles in the cytoplasm

dendrites (overall structure)

- processes off the cell body
- short, often highly branched
- tapered from base to tip

dendrites recieve

input from other neurons and sensory receptors

dendritic spines

small extension on the surface where synapses are formed

axons general shape

single process of the cell body with a constant diameter, but vary in length

cytoplasm of the axon

axoplasm, cytoplasm of the axon

plasma membrane of the axon

axolemma, plasma membrane of the axon

axon hillock

cone shaped area coming off the cell body, where you will find voltage gated ion channels

initial segment

formed by the narrowing of the axon hillock

trigger zone consists of

axon hillock and initial segment

the trigger zone is where

action potential is generated

presynaptic terminal

region at the end of the axon that house synaptic vesicles that house neurotransmitters

synapse

point of contact between the axon ending and its effector

functional classes of neurons

based on the direction of action potential conduction

Types of Neurons: Functional Classification

- sensory neurons
- motor neurons
- interneurons

sensory neurons

- afferent
- conduct action potentials toward the CNS

motor neurons

- efferent
- conduct action potentials away from CNS and toward muscles or glands

interneurons

conduct action potentials within the CNS

structural classes of neurons is based on

the number of dendrites

multipolar neurons (2)

- many dendrites and single axon
- dendrite number vary with varying branching

multipolar neurons location (2)

motor neurons of the PNS and most neurons within CNS

bipolar neurons (3)

- one dendrite and one axon
- dendrites are often specialized to receive stimulus
- axons conduct action potentials

Location of bipolar neurons

sensory organs (retina, nasal cavity)

pseudo-unipolar neurons

single process exits the body and divides into two branches that function as a single axon

two branches of pseudo-unipolar axon

central and peripheral processes

peripheral process

extends to the periphery and has dendrites that act as sensory receptors or communicate with sensory receptors

central processes

extend to CNS

most sensory neurons are

pseudounipolar

anaxonic neurons

- no axons, only dendrite
- brain and retina
- communicate using only graded potentials

glial cells of the CNS

astrocytes
oligodendrocytes
ependymal cells
microglia

astrocytes are

cytoplasmic processes extending from the cell body, foot processes cover blood vessels, neurons, and pia mater

astrocytes regulate the

composition of extracellular brain fluid by producing chemicals the promote formation of tight junctions between endothelial cells of capillaries to form the blood brain barrier

blood brain barrier

- controls substances that pass from blood into brain and spinal cord
- protects neurons from toxins
- allows nutrients and waste products to be exchanged
- prevents fluctuations in blood composition

astrocytes play a role in

response to tissue damage in the CNS (reactive astrocytosis)

reactive astrocytosis

- caused by injuries in the CNS
- astrocytes wall of injury site
-limit spread of inflammation
- limit regeneration of axons of injured neurons

astrocytes promote development of

synapses and help regulate synaptic activity by synthesizing, absorbing, and recycling neurotransmitters

ependymal cells line

ependymal cells line ventricles of the brain and central canal of the spinal cord

choroid plexuses

specialized ependymal cells and blood vessels located in regions of the ventricles that secrete cerebrospinal fluid

ependymal cells have (2)

- many cilia to move CSF
- extension of basale surface extend deep into brain and spinal cord

microglia

CNS specific immune cells

microglia become

mobilized and phagocytic in response to inflammation
- phagocytize necrotic tissue, microorganisms and other foreign substances

Oligodendrocytes

- form myelin sheaths
- cytoplasmic extensions wrap around multiple axons
- insulate axons

glial cells of PNS

Schwann cells and satellite cells

schwann cells form

myelin sheath in PNS, schwann cekk wraps around only one axon

neurilemma (sheath of Schwann)

outermost layer of each schwann cell, contains majority of schwann cell cytoplasm, nucleus, and organelles

satellite cells

- surround neuron cell bodies in sensory and autonomic ganglia
- provide support and nutrition
- protect neurons from heavy metal poisons

myelinated axon

- schwann cells (PNS) or oligodendrocytes wrap around axons
(have myelin sheath)
-myelinated axons have a white appearance

myelinated axon function

- forms layers of phospholipids with small amounts of cytoplasm
- protect and electrically insulate axons

gaps in myelin sheath

Nodes of Ranvier - gaps where there is no myelin sheath
schwann cells or oligodendrocytes extend across and connect

unmyelinated axons (3)

- not devoid of myelin
- rest in invaginations of Schwann cells or oligodendrocytes.
- protects axons

development of myelin sheath

- begins in late fetal development
- continues rapidly until end of first year of birth
- slows and continues after the first year of birth

multiple sclerosis is a

chronic disease of CNS, gradual loss of myelin sheath

multiple sclerosis effects

- slows transmission of action potential
- impairs control of skeletal and smooth muscle

gray matter contains

neuron cell bodies and dendrites

gray matter CNS

cortex: surface of brain
nuclei: clusters deep within the brain

Gray matter PNS

ganglia: neuron cell bodies