Test 3 ( Nervous Tissues)

Functions of the Nervous System

Sensory, Motor, Integrative, Executive functioning

Sensory

sense changes through sensory receptors (touch, vision, hearing, PH, O2, BP)

Motor

Responds to stimuli (muscles, glands)

Integrative

Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors (fuzzy on skin)

Executive functioning

mental activity, consciousness, memory

Nervous System Components

brain, spinal cord, nerves, sensory receptors

Subdivisions

Central nervous system + peripheral nervous system

Central nervous system

(CNS): brain + spinal cord

peripheral nervous system

(PNS): sensory receptors + nerves

Nerves

grouped by where they start/ finish (ex. cranial nerves + spinal nerves)
-enter: sensory info
-exit: motor response

Components of PNS

Sensory Receptors, nerves, ganglion, plexus

Sensory recpetors

ending with neurons/separate, specialized cells that detect temperature, pain .etc

Nerve

bundle of axons + sheaths that connects CNS to sensory receptors, muscles, glands

Cranial nerves

originate from brain; 12 pairs (bilateral)

Spinal nerves

originate from spinal cord; 31 pairs (bilateral)

Ganglion

collection of neuron cell bodies outside CNS (connection of neurons)

Plexus

extensive network of axons, and sometimes neuron cell bodies, located outside CNS

Divisions of PNS

Sensory (afferent), Motor (efferent)

Sensory

(afferent): transmits action potential from receptors towards CNS

Motor

(efferent): transmits action potentials from (away from) CNS to effectors (muscles, glands)

Sensory input

light, sound, touch, small, taste, temperature, pain, pressure. etc

Muscles

Skeletal, Cardias, Smooth

Skeletal

bones + movements

Cardiac

heart muscle

Smooth

can't control consciously (pupils, digestive tract)

Sensory divisions of PNS

Gathering information from external and internal environment
-General and Special Senses

General senses

receptors throughout the body (skin, thermoreceptors)

Special Senses

receptors in specific organs (vision, light, information)

Motor Divisions of PNS

Somatic Nervous System

Somatic Nervous System

CNS to skeletal muscles
-voluntary control
-single neuron system (inside spinal cord and axon target tissue)

Synapse w/ skeletal muscle

junction of a nerve w/ another cell ie. neuromuscular junction is a synapse between a neuron and skeletal muscle cell

Autonomic nervous system

(ANS): from CNS to smooth muscle, cardiac muscle and certain glands.
-involuntary control
-2 neuron system: first from CNS to ganglion; second from ganglion (effector)

Division of ANS

Sympathetic + Parasympathetic (active at opposite times)

Sympathetic

prepares body for physical activity (fight/flight)

Parasympathetic

regulates resting/vegetative function: digestion foods (rest/digest)

Enteric Nervous System

(ENS): plexuses within the wall of the digestive tract
-can control the digestive tract independently of the CNS, but still communicates w/ the CNS via ANS (parasympathetic and sympathetic neurons contribute to plexus)

Sensory

(ENS): monitor chemical environment + stretching of walls

Motor

(ENS): contracts smooth muscle + controls secretions of GI organs + endocrine cells (blood)

Neurons

/nerve cells: receive stimuli + transmit action potential signals to other neurons/effector organs
-cell body/ soma
-dendrites
-axons

Dendrites

input (cytoplasmic extensions) of neuron
-short, extensions of the cell body
-can interact with axons of other neurons

Axons

output (action potential)
-arises at the cone shaped axon hillock
-start of the axon: initial segment
-diameter is constant, but length can vary from mm up to 1m

Neuroglia

/glial cells:
-non-neural cells (no action potential)
-support and protect neurons

Axoplasm

cytoplasm around an axon

Axolemma

Membrane covering an axon

Presynaptic terminal

synaptic end bulb: terminal end

Vesicles

Neurotransmitters (chemical signal) in presynaptic terminal (synaptic vesicles)
-can release neurotransmitter to stimulate/ inhibit postsynaptic cell
- can move up and down the axon transporting neurotransmitter

Axonal transport

way disease can be transmitted to CNS (ie. rabies, herpes)

Functional classification

the direction of nerve impulse

Interneurons

(association neurons): within CNS from one neuron to another

Structural classification

Multipolar, Bipolar, Unipolar

Multipolar

many dendrites, single axon
-most neurons in CNS + motor neurons

Bipolar

1 dendrite, 1 axon- sensory organs
(ex. eye (retina), inner ear)

Unipolar

(pseudo-unipolar): single process extending from cell body - divides into 2 branches
-part extending to periphery has dendrites that typically function as sensory receptors

Supporting Cells of Nervous System

Neuroglia

Neuroglia

(glia, glial cells/neuroglial cells)
-nerve glue
-numerous - account for more than 50% of the weight of the brain
- 4 types of neuroglial cells in CNS
-2 types in PNS
-unique structure + function

Supporting Cells of the CNS

Astrocytes, Ependymal cells, microglia, oligodendrocytes

Astrocytes

(largest + most numerous)
-start shaped
-release chemicals to form tight junctions between endothelial cells of capillaries

Blood Brain Barrier

protects against toxic substances

Ependymal cells

(cuboidal/columnar shape)
-line the ventricles of the brain + central canal of spinal cord
-helps form the choroid plexus: produces CSF: cerebrospinal fluid
-patches contain cilia- help move CSF through ventricles

Microglia

(smaller + thinner)
-specialized macrophages in CNS
-phagocytic- inflammation
-dying tissue, microorganisms, foreign substances that invades CNS

oligodendrocyte

(smaller than astrocytes)
-cytoplasmic extensions: surround axons
-form myelin sheaths around portions of several axons

Supporting Cells of PNS

Schwann cells and Satellite cells

Schwann cells

(layers of phospholipid bilayer)
-wrap around axons
-forms myelin sheath around a portion of only 1 axon

Satellite cells

-surround neuron cell bodies in ganglia
-provides nutrients to cell body

Myelinated axons

covered by a myelin sheath, a multilayer of lipids and proteins
-conduct signals more rapidly than unmyelinated

Myelin

protects and insulates axons from one another

Unmyelinated axons

don't wrap around multiple times (single)
-small bit of protection

Organization of Nervous Tissue in CNS

Tract, Nucleus, White matter, gray matter

Tract

bundle of myelinated axons in CNS

Nucleus

collection of neuron cell bodies in CNS

White matter

myelinated axons
-nerve tract propagates action potentials from one area in CNS to another

Gray matter

-unmyelinated axons
-cell bodies
-dendrites
-neuroglia
-Integrative functions (decision making)

Spinal Cord

White is outer, gray is deeper

Brain

Gray is outer cortex, as well as inner nuclei; white is deeper