Se connecter

Se connecter avec OpenID

Chapter 48 Nervous System and Functions

Chapter 48: Nervous System
and Functions
Nervous system Components
• Neurons are the basic nerve cell or smallest entity of
- all animals groups except sponges have a neural
network of some kind
- differences aren’t the neurons but how they are
- Nerve nets serve most invertebrates for contraction
and expansion of cavity
- Cephalization involves clustering neurons near brain
to form more complex systems
*CNS (Central Nervous System ) – consists of brain and
spinal cord
*PNS (Peripheral Nervous System) – consists of
segmented clusters of neurons (ganglia) and nerves
that run throughout the body
Nervous Systems
Neuron Structure
• Neuron consists of 3 main structures:
Cell body – contains nucleus and organelles
Dendrites – branched extension of cell body that
receives signals from other neurons
Axons- extension from base of neuron that
transmits signal to other neurons
*Covered by a layer in segments called a
myelin sheath ( increases conduction speed)
• Synapse – space between end of one axon and
dendrite of next cell
- Neurontransmitters – chemical messengers that
navigate across synapse to continue message of neuron
Neuron Structure
Supporting Cells
• Glia – supporting cells necessary for integrity of
nervous system
Kinds of glia:
1. Astrocytes – provide structural support and
regulate concentrations of ions and
2. Radial glia – form tracks that give rise to CNS and
can serve as stem cells to generate new neurons
and glia
3. Oligodendrocytes and Schwann cells – form
the myelin sheaths around axons
*Multiple sclerosis – deterioration of myelin
sheaths and progressive loss of body
Supporting Cells
Info Processing
• 3 Stages of processing information:
1. Sensory input – sensory neurons transmit
along nerves (light, sound, touch, smell)
2. Integration – interneurons analyze inputs
and relay from brain to motor output
3. Motor output – motor neurons are effector
cells that act on response from body
Membrane Potential
• All cells have an electrical or voltage difference across
their plasma membrane known as membrane potential
• Resting potential – membrane of neuron that is not
transmitting signals
- refers to the passive diffusion of ions across the
Ex: Na and K in and out cell: Na/K pump
• Basis of all electrical signals in the nervous system is
that membrane potential can change from resting
when membrane’s permeability to an ion changes
Gated Ion channels
• Neurons can have gated ion channels which open
and close in response to stimuli
Stretch-gated – sense stretch and open when
membrane is mechanically deformed
Ligand-gated – messenger/receptor specific,
usually related to chemicals like neurotransmitters
found at synapses and bind to a channel
Voltage gated – open and close when
membrane potential changes
Gated Ion Channels
Action Potentials
• Action potential – all or none response that takes
place when membrane potential has reached its
*Gated channels open or close in response
to stimuli that changes membrane potential
- Na/ K channels are the main ions involved
in action potentials
- Normal resting potential is a negative
charge (-60 – 80 mV), due to constant
shuffling of potassium ions
Action Potential
• Depolarization occurs with membrane permeability
changing to open Na channels
- Na rushes into cell giving cell a positive charge
- Threshold is reached creating an action potential
send along the axon
• K channels that were inactivated change and open to allow
Potassium to leave the cell creating a negative charge or
Repolarizing effect
• Continued release of K from open channel eventually
causes a hyperpolarizing effect
- Na and K channels are closed causing a period of
inactivity known as a refractory period
Action Potentials
Conduction of Action Potentials
• Conduction can be long
distance signal
• Signal maintains strength
without diminish by
regenerating itself along
• Depolarization (Na)wave is
in one direction only;
followed by a
repolarization wave (K)
Speed of Signal
• Factors that contribute to conduction speed:
1. Diameter of axon – larger offers less
resistance – faster speed
2. Myelinated axons increase speed along
the nodes (Nodes of Ranvier)
- Saltatory conduction - signal jumps
from node to node regenerating the
depolarizing and repolarizing effect
Saltatory Conduction
Neuron Communication
• Information traveling from neuron to neuron has
two possible transmissions
1. Electrical synapses – contain gap junctions
and allow electric current to flow directly
from cell to cell
2. Chemical synapses – involve the release of
neurotranmitters that have been packaged in
synaptic vessicles, fuse with the membrane,
and by exocytosis cross the synaptic cleft to
post-synaptic cell
Direct Synaptic Transmission
• Direct transmission involved ligand gated ion
channels responding to specific
- binding to receptor opens or activates
channel allowing ions to diffuse across
- creates a postsynaptic potential by
changing membrane permeability
Direct Transmission
Two effects of postsynaptic potentials
1. Excitatory postsynaptic potentials
(EPSPs) – depolarization of membrane
nears threshold
2. Inhibitory postsynaptic potential (IPSPs)selective channels open creating a
hyperpolarizing effect that prevents
membrane from nearing threshold
• Unlike action potentials, PSPs are graded responses
• Signal strength diminishes and does not regenerate itself at
• PSPs also depend on amount of neurotransmitter released
• Summation refers to a process in which PSPs can add
together to near threshold and generate an action potential
or oppose the chances of threshold being near
Temporal summation – two or more EPSPs occur in
rapid succession from the same presynaptic neuron
before return to resting potential (near threshold)
Spatial summation – two or more EPSPs occur in
succession but from different presynaptic neurons
• Summation can happen in the same way with IPSP’s and
prevent a membrane from reaching threshold
Indirect Synaptic Transmission
• Neurotranmitters bind to a receptor not on
the ion channel and cause the activation of a
signal transduction pathway
- second messenger system has cascade of
reactions that create a slower onset but
longer lasting effect
- can be an amplified effect that opens or
closes many kinds of channels
Specialization of Nevous System
• Vertebrate CNS is derived from a nerve cord
which is hollow and develops into a central canal
in the spinal cord and ventricles within brain
- these hollow spaces are filled with cerebrospinal
fluid that aids in transport of nutrients, hormones and
removal of wastes
- also adds cushion to the brain
*White matter – of the brain refers to myelinated
*Gray matter – refers to cell bodies and dendrites
Peripheral Nervous System
• Consists of right-left pairs of cranial and spinal
12 pairs of cranial nerves that originate in the brain
and terminate in organs of head and upper body
31 pairs of spinal nerves that originate in spinal cord
and extend to many parts of the body
• Somatic nervous system is a function component
of the PNS that carries signals to and from
skeletal muscles in response to external stimuli
- Under conscious control or is voluntary
Peripheral Nervous System
Autonomic nervous system – another functional component
of the PNS; regulates internal environment by controlling
smooth, cardiac muscles, digestive organs, excretory and
endocrine systems
3 division of Autonomic nervous system:
1. Sympathetic – corresponds to arousal and energy
generation (adrenaline response)
2. Parasympathetic – counteracts acts of the
sympathetic division – calming and return to
3. Enteric – consists of neuron of digestive tract,
pancreas, and gallbladder
*controls organ secretions
Autonomic Nervous System
Brain Development
Brain stem consists of 3 parts:
1. Midbrain – integrated relay
center for sensory input (visual
and auditory)
2. Pons – involuntary functions
much like medulla, but also
regulation of functions in the
medulla (breathing)
3. Medulla oblongata –
involuntary visceral functions
like breathing, heart rate,
swallowing, vomiting, and
• Reticular formation – diffuse cluster
of neurons in brainstem the regulate
sleep and arousal
• Developed from part of metencephalon
• Functions include:
1. coordination and error checking with
motor functions
2. balance and movement
3. learning and remembering motor skills
4. Hand-eye coordination
• 3 main parts:
1. epithalamus – includes pineal gland
(melatonin); secretion in response to light
2. Thalamus – main input relay center for
sensory input to the cerebrum and motor info
3. Hypothalamus – control of hormone
release, homeostatic mechanisms including
hunger/thirst, basic survival mechanisms,
sleep/wake (biological clock), sexual and
mating behaviors
• Developed as outgrowth of forebrain and is divided into 2
- outer portion of gray matter; inner portion white
- largest and most complex portion of the brain
- sensory analyzing, motor commands, language
generation and interpretation
*Neocortex outermost portion that separates mammals
from other organisms – convoluted folds that increase surface
area but still fits inside the skull
• Each hemisphere corresponds to opposite side of the body
Ex: right hemisphere controls and receives input on left side of
• Corpus callosum – band of axons that serve as a communication link
between the 2 hemispheres
Lobes of Brain
• Cerebrum is divided into 4 lobes dealing with
sensory and motor inputs
1. Frontal lobe – olfactory sense; emotions;
2. Parietal lobe – somatosensory cortex dealing
with touch, pain, pressure, and temperature
3. Occipital lobe – primary visual cortex
4. Temporal lobe – auditory cortex; language
Information Processing
• Neurons of the somatosensory cortex and motor cortex
are distributed in an orderly fashion according to part of
body it corresponds to
*Cortical surface area devoted to each body part is not
related to size, but to the number of sensory neurons that
innervate it or the skill needed to control the muscles
Language and Speech
• Broca’s Area – located on left side of frontal
lobe near primary motor cortex controls
ability to formulate speech
• Wernicke’s Area – located in posterior portion
of temporal lobe that controls ability to
comprehend speech and language
PET of Language Mapping
• Limbic system – ring of structures found around
3 parts :
1. Amygdala
2. Hippocampus
3. Olfactory bulb
*system mediates feeling like laughing, crying,
aggression, feeding, and sexuality
• Also plays role in emotional memory
Memory and Learning
• Frontal lobe control mainly – short term memory – if
irrelevant is released
• Long term memory – frontal lobe control but also
incorporation of hippocampus
• Consolidation – transfer of short term to long term
Long term potentiation – increase in the strength
of synaptic transmission by brief high frequency
action potentials
- strengthens neural pathway of memory
- fundamental to learning
Без категории
Taille du fichier
1 492 Кб