Chapter 12 Nervous System: Nervous Tissue

What is the nervous system composed of?

1) brain

2) spinal cord

3) nerves

4) ganglia

5) nervous tissue 

What are the 2 cells that make up nervous tissue?

1) neurons

2) glial cells

What are neurons composed of?

-dendrites, cell body, axon

Function of Glial Cells 

-support and protect neurons 

3 Main Functions of Nervous System 

1) Sensory function 

2) Processing and integrating function 

3) Motor function 

Receptors

-belong to sensory function

-monitor change in internal and external environmental stimuli

What 2 body parts process and integrate sensory info?

1) brain

2) spinal cord

Brain and Spinal cord in Motor Function

initiate response as neurons relay motor info to effectors 

What do effectors include?

-all 3 muscle tissue

-glands 

What are some effects that effectors have?

-can be muscle contraction/relaxation

-change in gland secretion activity

Structural Organization of CNS 

-brain enclosed by skull 

-spinal cord protected within vertebral canal 

Peripheral Nervous System Structural Organization

-nerves

-ganglia

Nerves

bundles of axons of neurons extending from brain and spinal cord

Ganglia

-clusters of neuron cell bodies located along nerves

2 Divisions of nervous system

1) sensory nervous system

2) motor nervous system

Sensory Nervous System (afferent)

-detects stimuli by receptors and relays to the CNS (sensory input)

2 subdivisions of sensory nervous system

-somatic sensory

-visceral sensory 

Somatic Sensory

detect stimuli that we consciously perceive

Receptors of Somatic Sensory System

-receptors associated with the 5 senses

-proprioceptors (receptors in muscles, tendons, joints to detect body position) 

Visceral Sensory Components

-detect stimuli that we don’t consciously perceive in BVs and internal organs 

Examples of Visceral Sensory Detection 

-stretch of organ wall 

-chemical composition of blood 

Motor Nervous System (efferent)

-controls effectors

-initiates and transmits information from CNS to effectors (motor output) 

Motor Nervous System 2 Subdivisions

1) somatic

2) visceral

-based upon whether the effector can be controlled consciously

Somatic Motor Component 

-initiates and transmits motor output from CNS to skeletal muscles 

What is the only effector that can be voluntarily controlled? 

-skeletal muscles 

Autonomic Motor Component

-innervates and regulates other effectors that can only be involuntary controlled 

What are the effectors that are involuntarily controlled?

-cardiac muscle

-smooth muscle

-glands

2 subdivisions of autonomic motor component

-sympathetic division

-parasympathetic division 

A nerve is an…?

-organ, 2 or more tissue types work together to perform a function

Fascicle

-bundle axons

-numerous are present within a nerve

What type of muscle tissue are nerves similar to?

-skeletal muscle

3 connective tissue wrappings of nerves

1) epineurium

2) perineurium 

3) endoneurium 

Epineurium 

-thick layer of dense irregular CT enclosing the nerve 

-protects and supports entire nerve

Perineurium

-layer of dense irregular CT wrapping each fascicle

-protection and support to bundle of axons

-supports BVs

Endoneurium

-areolar CT surrounding each axon

-separate and electrically insulate each axon 

Nerve Vascularization 

-branch and extend through epineurium and perineurium to become capillaries in endoneurium

BVs in Nerves Function

-site of exchange of substances between the blood within capillaries and axons

Cranial Nerves

-extend from the brain

-structural classification

Spinal Nerves

-extend from spinal cord

-structural classification 

Sensory Nerves

-contain only axons of neurons

-relay info from receptors towards CNS (sensory neurons)

Motor Nerves

-contain axons of neurons

-relay info away from CNS to effectors (motor neurons)

Mixed nerve

-contains both sensory and motor axons (still transmit in their designated directions away/to the CNS)

Nerve 

-a bundle of axons in the peripheral nervous system 

Ganglion 

-cluster of neuron cell bodies in peripheral nervous system (causes swelling) 

2 types of ganglia

1) posterior (dorsal) root ganglia associated with sensory neurons extend into spinal cord

2) associate with motor neurons extend to autonomic effectors (cardiac/smooth muscle, glands) 

Neuron

-transmit electrical signals

-release neurotransmitters

3 characteristics of neurons

1) excitability

2) conductivity

3) secretion

Excitability

-ability of cell to respond to stimulus

What does a stimulus cause?

- local voltage change in resting membrane potential due to movement of ions across membrane of cell 

Conductivity

-voltage changes along membrane as voltage-gated channels open 

Secretion

neurons release neurotransmitters in response to conductivity

Neurotransmitters

-molecules stored in vesicles and released when bound to a cell

-excitatory/inhibitory effect

What is excitability associated with?

-dendrites and cell body

What is conductivity associated with?

axon

What is secretion associate with? 

-synaptic knobs 

Neuron Longevity 

-form during fetal development and continue to function over lifetime 

Neuron Mitotic Ability 

-neurons lose ability to form new cells by mitosis 

2 Exceptions of Neuron Mitotic Ability

-neurons in hippocampus

-olfactory epithelium of nose

Neuron Cell Body (Soma) Shape

-spherical shape with cone region called axon hillock 

What does the Cell Body house?

-nucleus and cytoplasm

Nucleus in the Cell body

-contains chromatin and nucleolus to synthesize ribosomes 

Cytoplasm in Cell Body

-called the perikaryon

-composed of the typical organelles