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the master controlling and communicating system of the body
functions of the nervous system?
- sensory input
- Motor output
What is sensory input?
monitoring stimuli occurring inside and outside the body
What is integration?
The interpretation of sensory input
What is motor output?
The response to stimuli by activating effector organs
What are the two major sections in the nervous system?
- The central nervous system
- Peripheral nervous system
- paired spinal and cranial nerves
- carries messages to and from the spinal cord and brain
- everything else that is not the central nervous system
Central Nervous system?
- Brain and spinal cord
- integration and commander center
- the middle
The Peripheral System can be divided into what 2 sections?
Sensory division and Motor division
- sensory afferent fibers- carry impulses from skin, skeletal muscles, and joints to the brain
- Visceral afferent fibers- transmit impulses from visceral organs to the brain
- transmit impulses from CNS to effector organs
The motor division can be divided into what?
- Somatic nervous system
- Autonomic nervous system
Somatic nervous system?
conscious control of skeletal muscles
Autonomic nervous system?
- Regulates smooth muscles, cardiac muscle, and glands
- divisions- sympathetic and parasympathetic
What are the two principal cell types of the nervous system?
- excitable cells that transmit electrical signals
- most communication is done by them
what are neuroglia or glial cells?
- They are the supporting cells in the nervous system
- cells that surround and wrap neurons
What are the functions of Neuroglia?
- provide support scaffolding for neurons
- segregate and insulate neurons
- guide developing neurons to the proper connections
- promote health and growth
What are dendrites?
- short, tapering, and diffusely branched processes
- they are the receptive, or input, regions of the neuron
- electrical signals are conveyed as graded potentials
- they get signals from other neurons
What is an axon hillock?
- cone-shaped area from which axons arise
- That is where the action potential comes from
the insolation sheet made of myelin that insulates the axon in the PNS
What is axon?
Where the cell sends a signal
What is the Soma?
- The nerve cell body
- It cannot divide
- Biosynthetic (making things for life)
- Focal point for the outgrowth of neuronal processes(dendrites/axons)
- Axon hillock
What is the difference between a graded potential and an action potential?
- Graded- vague electrical signal
- Potential- direct and strong enough to be sent to another neuron
What are the main two functions of an axon?
- generate and transmit action potentials
- they secrete neurotransmitters from axonal terminals
- branches terminus of an axon
- signals will exit through it
What is the function of the myelin sheath?
- protect the axon in the Peripheral Nervous System
- electrically insulate fibers from one another
- increase the speed of the nerve impulse transmission
What are the Nodes of Ranvier?
gaps in the myelin sheath between adjacent Schwann cells
What is Neurilemma?
the nucleus and cytoplasm in a Schwann cells
Schwann cells are in which nervous system?
The Peropheral Nervous Sytem
- makes the myelin sheaths in axons in the CNS
- There is no neurilemma
- and the Nodes of Ranvier are widely spread
- there is no neurilemma
Regions of the Brain and Spinal Cord?
- White matter- dense collections of myelinated fibers
- Gray matter- mostly soma and unmyelinated fibers (not as dense)
Neuron structural Classification?
- Multipolar- three or more processes (most common
- bipolar- two processes
- unipolar- single, short process
Neuron Functional classification?
- Sensory (afferent)- transmit impulses toward the CNS
- Motor (efferent)- carry impulses away from CNS
- Interneurons (associations neurons)- shuttle signals through CNS pathways
Action potentials or nerve impulses are what?
always the same regardless of stimulus
measure of potential energy generated by separate charge (how much electrical energy there is)
voltage measured between 2 points (the difference of energy in 2 places)
the flow of electrical charge between 2 points
hindrance to charge flow (how much it will take to stop a current)
Substance with high electrical resistance
- substance with low electrical resistance (they transmit energy)
- ex. wires
Electrical Current in the body?
- Flow of ions rather than electrons
- Na+, K+, Cl-
- When there number of ionic charges is difference across the membrane.
- K+ leaks out (diffusion) Inside becomes negative and outside becomes positive
- The membrane provides a resistance to ion flow
High permeability= ?
Low permeability= ?
Low resistance, high resistance
Most cells have a resting potential of what?
A membrane potential is measured....
relative to the intercellular charge (negative in a resting cell(
The resting potential difference (-70mV) is generated by what?
the concentration gradients of Na+, K+, Cl- and protein (A-)
Ionic differences (resting potential) are consequences of what?
- Differential permeability Na+ and K+ (whether there is resistance)
- Operation of the sodium- potassium pump (letting things through)
Chemical gradient: sodium-potassium pump?
results in an unequal distribution of ions across the plasma membrane. K+ in Na+ out
How does the Sodium- potassium pump work?
- While K+ is being leaked out Na+ us being pumped in
- But then there is a pump that pushes K+ in and Na+ out to not reach equilibrium and keep a resting membrane (-70mV)
What are the 3 main things to consider during the initiation and propagation of nerve impulses?
- ion channels
- membrane potential
- the effects of each on one another
What is the different kinds of ion channels?
- passive, or leakage, channels- always open
- chemically gated channels- open with binding neurotransmitter
- voltage gated channels- open and close in response to membrane potential (electrical charge)
- mechanically gated channels- open and close in response to physical perturbations of receptors
How do neurons communicated with one another?
- through chemically gated channels.
- When neurotransmitter binds to the receptor it changes the shape of the protein channel and things can come in and out
When the protein channels change cause of something touched it or bumped into it
How are voltage changes created?
When gated channels are opened, ions diffuse across the membrane through the channel, movement is along their chemical gradients, an electrical current of ions is created and the voltage changes across the memebrane
membrane potentials are produced by?
- Changes in the membrane permeability to ions via Voltage gated channels
- Result in alterations of ion concentrations across the membrane
types of signals
- graded potentials
- action potential
the inside of the membrane becomes less negative
the inside of the membrane becomes more negative than the resting potential (-70mV)
the return of the membrane to its normal resting membrane potential (-70mV)
- Can only travel short distances
- decrease in intensity with distance
- their magnitude varies with the strength of stimulus
- sufficiently strong graded potentials can initiate action potentials
- only generated by muscle cells and neurons
- they do not decreases in strength over sistance (cause of myolin sheath)
- they are the principal means of neural transmission
An action potential of a neuron is what?
a nerve impulse
Both Na+ and K+ channels are closed
- Na+ channels open
- K+ channels close
- The membrane potential becomes less negative
- Na+ closes
- K+ open to make the inside less positive
Sometimes Na+ comes in but K+ rushes out fast to try to get to -70 mV
What is the purpose of of the Sodium-Potassium Pump?
to restore resting condition by kicking out Na+ and bringing back in K+
When graded potentials sum to approximately -55mV
What happens when a grade potentials reach a threshold potential?
It triggers action potentials
What is a refractory period?
- It ensure that each action potential is separate
- It enforces one-way transmission of nerve impulses
- Prevents muscle lock ups
Why is tetrodoxin bad?
- it blocks sodium V-gated sodium channels and inhibits nerve impulse generation
- One becomes paralized
membrane is depolorized by 15 to 20mV
Strong stimuli can generate what more often than a weak stimuli?
Stimuli intensity is determined by what?
the frequency of impulse transmittion
The rate of impulse propagation is determined by what?
- axon diameter
- presence of a myelin shealth
the larger the diameter, the faster the impulse
presence of myelin sheath?
myelination dramatically increases impulse speed
The current passes through a myelinated axon only where?
the Nodes of Ranvier
action potentials are triggered where?
Nodes of Ranvier and jump from one node to the next
Conduction of current is faster in what?
myelinated axons than numyelinated axons
- a junction that mediates information transfer from one neuron:
- to another neuron
- to an effector
conducts impulses toward the synapse
transmits impulses away from the synapse
release and reception of neutransmitters
what are chemical synapses composed of?
- axonal terminal of the presynaptic neuron which contain synaptic vesicles
- receptor region on the dendrite or soma of the postsynaptic neuron
fluid filled space that prevents direct transmission of nerve impulses
What is a transmission across the synaptic cleft?
- is a chemical event (not electrical)
- ensures unidirectional communications between neurons
How does the synaptic cleft transfer information?
- Graded potential signals the soma
- The soma fires an action potential
- Action Potential goes down the axon to axonal terminal and signals Ca release
- That causes release of neurotransmitters into the synaptic cleft and bind to receptors on postsynaptic neuron
- Then postsynaptic membrane permeability changes causing an excitatory or inhibitory effect
When some neurotransmitters get stuck in the presynaptic neuron instead of going to the postsynaptic neuron
How are neurotransmitters removed?
- enzymes degrade them
- they are reabsorbed by astrocytes or presynaptic terminals
- they diffuse from synaptic cleft
Channel- linked receptors?
- composed of integral membrane proteins
- control neurotransmitter action
- chemically gated channels
- causes graded potentials
- depolarize membranes
- only in chemically gated channels
- can initiate Action Potentials
- diffusion of Na+ into cells causes local depolarization
- causes membrane to become more permeable to potassium and chloride
- makes inside more negative
- reduces the chance of an action potential
Where are voltage gates?
in the hillock (the starting point of Action Potential)
graded potentials are summed to either depolarize or hyperpolarize a postsynaptic neuron
presynaptic neuron transmit impulses in rapid fire order (many have to add up until an action potential happens)
postsynaptic neuron is stimulated by a large number of terminals at the same time ( a bunch of them fire at once and make an action potential)
chemicals used for neuronal communication with the body and the brain
neurotransmitters releases during muscle contractions