Transcript Nervous System and Senses - Avon Community School Corporation


Sensors
› Monitor external and internal environment

Processing
› Receives information, integrates it, and decided
what to do

Effectors
› Carries messages to effectors and tells them
what to do

Neurons
› Main cell of nervous tissue
› Relay and process messages

Neuroglial
› Provide support to the neurons
› Several types known
› Ex: Schwann, microglial

Microglial cells
› Scattered throughout CNS
› Phagocytize bacteria or cellular debris

Oligodendrocytes
› Along nerve fibers
› Provide myelin sheath (made of a fatty
substance called myelin) around axon in CNS

Schwann cells
› Same as oligodendrocytes but in PNS

Astrocytes
› Provide connection between a neuron and a
blood vessel
› Provide support, help regulate ion concentrations
in tissue, make-up scar tissue after injury

Ependymal cells
› Forms epithelial-like linings on the outsides of
specialized parts or lining cavities within the CNS
Remember: It’s a cell!
 Body of neuron

› Cell Body – contains cell organelles
› Dendrites- carry messages to cell body
› Axons – carry messages away from cell body

Cell Structures
› Large nucleus with easily seen nucleolus
› Chromatophilic substance – similar to rough ER
 Scattered throughout cytoplasm, membranous
› Neurofibrils- help support cell shape
Can be myelinated or unmyelinated
 PNS

› Schwann cells form myelin sheath
› Nodes of Ranvier- small breaks in myelin sheath

CNS
› Oligodendrocytes form myelin
› Myelinated neurons form white matter
› Unmyelinated neurons form gray matter

Multipolar
› Many small branched dendrites
› One axon
› Found in CNS

Bipolar
› Two processes off of cell membrane (one axon and
one dendrite)
› Neurons in special sense organs

Unipolar
› One process off of cell body (one axon)
› Found throughout PNS

Sensory (afferent) neurons
› Have sensitive dendrites that are stimulated by
changes in environment
› Message is taken into CNS
› Usually unipolar or sometimes bipolar

Interneurons
› Transfer, direct, and process messages within CNS
› Usually multipolar

Motor (efferent) neurons
› Carries message out of CNS to effectors
› Usually multipolar

Inside the neuron
› High in K+
› High in negative ions

Outside the neuron
› High in Na+
› High in positive ions

Result
› K+ tends to diffuse out
› Na+ tends to diffuse in
› Negative ions cannot cross
Na/K pump - helps to restore concentration
gradient across the cell membrane
 Resting potential - difference is electrical
charge across the membrane

› Established by concentration gradients of
various ions
› Inside of the membrane has a negative charge
of 70 mv
› Membrane is said to be polarized
Stimuli cause changes to the resting
potential by making the inside of the
membrane less negative
 Once a stimulus happens:

› If stimulus is not strong enough to reach
threshold potential = cell membrane will return
to resting potential
› If stimulus is strong enough to reach threshold
potential = start an action potential

Summation - when additive effect of stimuli
causes action potential
Starts at trigger zone of axon
 Threshold stimulus open sodium channels
 Sodium moves into axon

› Because of the concentration gradient
› Because of the negative charge that attracts the
positive ions
Depolarizes the membrane as negative charge
diminishes
 Potassium channels open and potassium moves
out of the axon, repolarizing the membrane
 Animation #1
Animation #2

Action
Potential
Animation
Action potential at the trigger zone stimulates
the next part of the axon to do a action
potential
 Potentials spread along the axon like a wave
 Unmyelinated axons

› Wave continues uninterrupted; relatively slow

Myelinated axons
› Wave goes through saltatory conduction (jump from
one node to the next); very fast
Animation

All-or-nothing effect
› Neuron does not react until a threshold stimulus
is applied, but once it is applied it reacts fully
Stimuli greater than threshold levels don’t
change the size of the response but changes
its frequency
 Refractory period:

› After a action potential
› Brief period of time
› The nerve cannot be stimulated again.
The connection between two neurons
 Don’t touch, separated by synaptic cleft
 One-way communication between axon of
presynaptic neuron and dendrite of
postsynaptic neuron
 Neurotransmitters are made in the synaptic
knob of the axon, stored in synaptic
vesicles, and cross the cleft when needed


Excitatory Action:
› A neurotransmitter that puts a neuron closer to
an action potential (facilitation) or causes an
action potential

Inhibitory Action:
› A neurotransmitter that moves a neuron further
away from an action potential

Response of neuron:
› Responds according to the sum of all the
neurotransmitters received at one time
Acetylcholine
 Monoamines – modified amino acids
 Amino acids
 Neuropeptides- short chains of amino acids
 Depression:

› Caused by the imbalances of neurotransmitters

Many drugs imitate neurotransmitters
› Ex: Prozac, zoloft, alcohol, drugs, tobacco
When an action potential reaches the end of
an axon, Ca+ channels in the neuron open
 Causes Ca+ to rush in

› Cause the synaptic vesicles to fuse with the cell
membrane
› Release the neurotransmitters into the synaptic
cleft

After binding, neurotransmitters will either:
› Be destroyed in the synaptic cleft OR
› Taken back in to surrounding neurons (reuptake)

Animation
Groups of highly interconnected neurons
that work together in the CNS
 Convergence

› Axons from different parts of the nervous
system connect to the same neuron combining
their affects

Divergence
› A message from one neuron is sent to many
neurons at once; amplifies message
Divergence
Convergence
Nerves are made of bundled axons, called
nerve fibers
 Nerve fibers

› Sensory (afferent)- carry messages to CNS
› Motor (efferent)- carry messages from CNS to
effectors

Nerves
› Same definitions hold true
› Most nerves contain both types of fibers and are
called mixed nerves
A nerve fiber (axon) is surrounded with
endoneurium
 Nerve fibers are bundled together and
surrounded with perineurium to form a
fascicle
 Fascicles are bundled together and
surrounded with epineurium to form a
nerve

Path that the message
takes through the body
 Includes:

› Sensor
› Sensory neuron
› Interneuron
› Motor neuron
› Effector
Simplest nerve pathway is a reflex
 Reflexes without pain

› Involve only sensory and motor neurons
› Ex: knee-jerk reflex

Reflexes with pain
› Involve interneurons
in CNS
› Ex: withdrawal reflex
Central nervous system
 Consists of brain and spinal cord
 Made of both gray and white matter
 Covered in meningies

Cranial Bone
 Dura mater

› First layer; tough, fibrous connective tissue
› Forms inner periosteum of cranial bone
› Folds into the cranium in some places to form
division walls in the brain

Arachnoid mater
› Web-like membrane over CNS
› Does not dip into crevices

Subarachnoid space
› Below arachnoid layer
› Contains cerebrospinal fluid

Pia mater
› Lower layer of meninges
› Forms a tight covering over brain
› Does dip into crevaces

Same except:
› Vertebrae bones - protection
› Epidural space- filled with loose connective and
adipose tissue
› All other are the same
Flows through ventricles (spaces in brain) in
the subarachnoid space, and through the
central canal of the spinal cord
 Fluid is made by the choroid plexus

Stretches from brain to intervertebral disk
between first and second lumbar vertebrae
 31 pairs of spinal nerves come of the cord
 Gray matter core surrounded by white
matter

Responsible for communication between
brain and body and spinal reflexes
 Ascending tracts

› Nerves that send info to brain

Descending tracts
› Nerves that send into to effectors
Made up off about 100 billion neurons
 Four main sections:

› 1) Cerebrum
 Nerves for processing sensory and motor function
 Higher functions (like reasoning)
› 2) Diencephalon
 Processes sensory information
› 3) Brainstem
 Regulates certain body functions like breathing
› 4) Cerebellum
 Coordinates skeletal muscle movements
Divided into two hemispheres: right and left
 Corpus callosum

› Connects the two sides

Other structures
› Convolutions - ridges
› Sulcus - shallow groove
› Fissure - deep groove
Frontal lobe
 Parietal lobe
 Temporal lobe
 Occipital lobe
 Insula


Each lobe has unique functions

Cerebral cortex
› Thin layer of gray matter surrounding cerebral
hemisphere; contain most of the cell bodies in
the cerebrum

Inner part of the cerebrum is mainly made
of white matter

Motor areas
› Primarily in frontal lobe
› Send information out to effectors

Sensory areas
› Interpret information from sensors
› Area in parietal, temporal, and occipital lobes

Association areas
› Analyze information from sensors
› Located in areas in all lobes mentioned above
Located between the cerebral hemispheres
above the brainstem
 Contains:

› Thalamus
› Hypothalamus
› Pituitary gland
› Pineal gland

Thalamus
› Routes sensory impulses to the correct region of
the cerebrum

Hypothalamus
› Monitors many internal conditions, link between
nervous and endocrine system

Limbic system
› Thalamus, hypothalamus, and basal nuclei
› Controls experience and expression (feelings)
Connection between spinal cord and the
rest of the brain
 Contains:

› Midbrain
› Pons
› Medulla oblongata
Located between diencephalon and pons
 Contains some visual and auditory reflexs
 Serves as the main connection for motor
neurons between spinal cord and upper part
of brain

Rounded bulge between midbrain and
medulla oblongata
 Relays impulses between medulla and
cerebrum or between cerebrum and
cerebellum

Lowest part of brain, connect to spinal cord
 All ascending and descending tracts run
through the oblongata
 Serves as a control center for many vital
function like heart rate, blood pressure,
and respiratory center

Located in the lower back part of the brain
 Structured liked cerebrum with inner white
matter core and gray matter covering
 Controls posture and complex skeletal
movements

Peripheral Nervous system
 Includes:

› 12 pairs of cranial nerves
› 31 pairs of spinal nerves

Divided into:
› 1) Somatic nervous system
 Controls conscious activities; connects to skin and
skeletal muscles
› 2) Autonomic nervous system
 Controls unconscious activities; connects to
internal organs or structures

Two branches:
› 1) Parasympathetic
 Control under more normal conditions
› 2) Sympathetic
 Control under stress or emergency conditions
(fight or flight)

Usually these have antagonistic effects
› Work to counteract each other (one increases,
while other decreases)

Either might be utilized to maintain
homeostasis