1.2 A Nervous System Organization

neuron

excitable cells

gilal cells

non-excitable, mitotic support cells found in both the CNS and PNS (contain different kinds tho)

critical for normal function at neural synapses

what are the central and peripheral nervous systems made out of

nervous tissue

nervous tissue

neurons and gilal ccells

are there more gilal or neurons

glial cells account for about 1/2 of the entire volume of the nervous system

nerves

only found in the PNS are organs composed of clusters of numerous neuron axons

Central Nervous System

contain the brain and spinal cord

bbrain in regards to the central nervous system

site of thoughts and intelligence

processes information received and sends messages back to the body

Spinal cord in regards to the central nervous system

carries information between the brain and the body

musculoskeletal reflex center … like knee jerk

What protects the central nervous system

covered by connective tissue meninges

protected by skull and vertebrae

peripheral nervous system

nerves and ganglia

nerves in regards to peripheral nervous system

bundled axons which carry signals to and from the CNS

extended from brain or spinal cord

ganglia in regards to the peripheral nervous system

cluster of neuron cell bodies outside of the CNS

Nerve

an organized collective bundle of neuron axons that send signals throughout the PNS

How are nerves classified

structuarally by location or functionally based on the direction of signals they carry

types of nerves classified structurally by location

cranial nerves that extend from the brain

spindal nerves that extend from the spinal cord

nerves that are classified functionally based on the direction of signals they carry

• sensory nerves

• motor nerves

  • mixed nerves

sensory nerves

carry afferent sensory signals from the receptors throughout the body to the CNS (brain or spinal cord)

Motor nerves

carry EFFERENT motor signals from CNS (brain or spinal cord) to the effector ( skeletal muscles, smooth muscles and glands)

Mixed nerves

Carry both afferent sensory and efferent motor signals

• all spinal nerves are mixed nerves

sensory signals are (afferent or efferent)

afferent - inward to cns

motor signals are (afferent or efferent)

efferent - outward

epineurium

connective tissue surrounding the outer nerve surface, protects the nervep

perineurium

connective tissue that surrounds and separates bundles of axons organized into fascicles

location of blood vessels supplying the nerve

endoneurium

connective tissue that surrounds and separates individual axons both unmyelinated or myelinated within fascicles

provides electrical insulation

Ganglion

localized cluster of neuron cell bodies and associated glial cells , found along the length of a nerve in PNS

Afferent Pathway branches

sensory nervous system to somatic and visceral sensory

efferent pathway branches

motor nervous system into somatic motor and autonomic motor - which further branches into sympathetic and parasympathetic division

Sensory nervous system

• detects stimuli and transmits information from receptors to the CNS

detects stimuli and transmits information from receptors to the CNS

Somatic nervous system

branches from the sensory nervous system

• sensory input that is consciously perceived from receptors

visceral sensory

• branches from sensory nervous system

sensory input that is not consciously perceived from receptors of blood vessels and internal organs

Motor Nervous system

output

• initiates and transmits information from the CNS to effectors

Somatic Motor

motor output that is consciously or voluntarily controlled… effector is skeletal muscle

e

effector of somatic motor

skeletal musclea

autonomic motor

motor output that is not consciously or is involuntarily controlled

effectors are cardiac muscle smooth muscle and glands

effectors of autonomic motor

cardiac muscle smooth muscle and glands

sympathetic division

branches from motor nervous then autonomic motor

best known for fight or flight or freeze stress response

parasympathetic division of autonomous motor

often referred to as the resting and digesting branch due to its role maintaining homeostasis

structural classification of neuron types

multipolar, bipolar, unipolar and anaxonic

multipolar neuron

most common type of neuron

includes all motor neurons and most interneurons

multiple processes extend directly from neuron cell body (soma)

typically has multiple dendrites and one axon

includes all motor neurons and most interneurons

what is the most common type of neuron

multipolar neuron

what are all motor neurons and most interneurons

multipolar neurons

bipolar neuron

limited locations

found in some special senses like retina and olfactory epithelium in nose

two processses extend directly from cell body - one dendrite and one axon

Unipolar neuron

• most sensory neurons

dendrites directly to peripheral process of axon… single short process extends directly from the cell body and forms a T intersection with the two processes (peripheral and central) of one long axon.

anaxonic neuron

• interneurons

  • lacks an axon; processes are only dendrites that extend from cell body

sensory neurons

receive somatic and visceral sensory input

conduct action potential signals to the CNS

most sensory neurons are unipolar with receptive region and cell body in PNS and axon ends in the CNS

dendrites

receive nerve impulses… transferring them from synapse to the cell body

axons

long thread like portion of a nerve that carries nerve impulses away from the cell body

Interneuron (association neurons)

receives signals from sensory neurons and sends signals to motor neurons

• locate entirely in the CNS

  • typically multipolar or anaxonic neurons

motor (association) neuron

conducts motor output from cns to effectors in the PNS…

innervates both somatic and autonomic effectors

multipolar neurons

Types of synapses

electric and chemical synapses

electrical synapse

fastest type of synapse

junction between two neurons that allow for the two way transmission of electrical signals

presynaptic and postsynaptic neurons bound together by gap junctions

chemical synapses

most common type of synapse

presynaptic neuron’s axon terminal produces signal iin the formaof a neurotransmitter

post synaptic neuron recieves signal as a neurotransmitter binds to receptors and causes a postsynaptic potential … either depolarization or hyperpolarization)

types of axonal transport

retrograde and anterograde

anterograde transport

moves newly synthesized material toward synaptic knobs

retrograde transport

moves used material from axon for breakdown and recycling in celll body

Fast axonal transport

approx 400 mm/day

involves movement along microtubules powered by motor proteins that split ATP

anterograde transport of vesicles, organelles, glycoproteins

retrograde transport of used vesicles, potentially harmful agents

slow axonal transport

result from the flow of axoplasm

• anterograde transport of enzymes, cytoskeletal components, new axoplasm