Chapter 9 - Nervous system

• Nervous system - organ system that includes the brain, spinal cord, nerves and sense organs; all of which controll all body functions

  A) sensory

  B) effector

  
• Types of cells that form nervous tissue:

  • Neurons
  • they conduct signals/ impulses
  • neuroglia
  • provide protection, support, insulation and nutrients for neurons
• peripheral nervous system (PNS):

  • includes cranial and spinal nerves that connect the CNS to other body parts
  • is separated into sensory and motor divisions
  • sensory (afferent) division brings info to the CNS and they monitor external factors (like light and sound intensities)
  • motor (efferent) division conducts impulses from CNS to the effectors
  • motor functions have 2 categories
  • voluntary - inc the somatic nervous system, which controls skeletal muscle
  • involuntary - inc the autonomic nervous system, which controls involuntary effectors; like cardiac and smooth muscle and many glands
• central nervous system (CNS):

  • consists of brain and spinal cord
  • the signals are integrated (brought together for processing) from various sensory receptors for coordination and processing
• Nervous system organisation:

  A) central nervous system

  B) peripheral nervous system

  C) afferent

  D) efferent

  E) somatic

  F) autonomic

  
• Structural classification of neurons:

  • multipolar neurons
  • one axon and many dendrites
  • mainly found in brain and spinal cord
  • many processes arising from their cell bodies
  • bipolar neurons
  • only have 2 processes
  • one is an axon and one is a dendrite
  • mainly found in eyes, nose and ears
  • unipolar neurons (psuedounipolar)
  • single process
  • had 2 branches that work together as one axon
  • mainly found in ganglia (outside brain and spinal cord)
• Structural classification of neurons

  A) bipolar

  B) multipolar

  C) unipolar

  D) multipolar

  E) unipolar

  F) bipolar

  
• Neuron structure

  A) dendrites

  B) neurofilaments

  C) nodes of ranvier

  D) myelin

  E) schwann

  F) cell body

  G) axon

  
• Neuron Structure:

  • vary in size and shape
  • have 3 distinct regions - cell body, dendrites and axon
  • cell body
  • contain most organelles
  • contain protein fibers (neurofilaments) that maintain shape of the cell and ensure proper diameter of axon (important for impulse conduction)
  • dendrites
  • provide surface area to recieve communications from other neurons
  • highly branched
  • axon - send impulses away from cell body to other cells
  • nodes of ranvier - gaps in myelin sheath along mylinated neurons
• Functional classification of neurons:

  • sensory neuron
  • conduct impulses from the peripheral body parts into the brain or spinal cord
  • sensory receptors to the CNS
  • most are unipolar some are bipolar
  • interneurons
  • conduct impulses from one part of the brain or spinal cord to another
  • often connect sensory and motor neuron
  • they are multipolar and link other neurons
  • motor neurons
  • conduct impulses from the CNS to effectors
  • they are multipolar
• Functional classification of neurons:

  A) sensory neuron

  B) interneuron

  C) motor neuron

  D) efferent

  E) muscle

  F) afferent

  G) afferent

  H) efferent

  I) peripheral

  J) central

  
• Neuroglia:

  • a collective term for 6 types of cells (4 in CNS and 2 in PNS)
  • functions include protection, insulation and general support
• Neuroglia in the CNS:

  • microglia - spider shaped, develop from monocytes (white blood cells), phagocytize bacterial cells and cellular debris
  • oligodendrocytes - produce myelin
  • astrocytes - connects neurons to blood vessels, make up to 90% of all cells in certain areas of the brain
  • ependymal - line ventricles of the brain and the central canal of the spinal cord
• Neuroglia in the PNS:

  • schwann cells - produce myelin sheath that surrounds axons of peripheral nerves
  • satellite cells - provide protective coat around the cell bodies of peripheral neurons
• Neuroglia in the CNS and the PNS:

  A) ependymal

  B) astrocyte

  C) microglial

  D) oligodendrocyte

  E) satellite

  F) schwann

  
• polarity = differences in electric charge in a given area (most cells are negative on the inside and positive on the outside)
• Membrane potential and distrubution of ions:

  • resting membrane potential = the resting charge inside a neuron (or when inactive) is about -70mV
  • changes arise from ions
  • K+ is found in high conc on the inside of a neuron and Na+ is found in high conc outside the neuron
  • the overall charge inside the neuron is due to phosphates and sulfate anions - they are known as 'fixed' anions as they can't cross the cell membrane
  • conc gradient of Na+ and K+ set the stage for a neuron to be excited and rapidly get back to rest

  A) potassium

  B) sodium

  
• Stimulation and the action potential:

  • the neuron will rest until stimulated by a stimulus
  • action potential = rapid change in the membrane potential
  • 1st in a positive directions, then a negative direction and then back to resting potential
  • threshold stimulus = stimulus that will cause inflow of Na+ enough to change the membrane to -55mV
  • threshold potential = stimulation level that must be achieved to elicit an action potential
  • All or none response = an action potential is either achieved (all) or it is not (none)
• Action potential steps:

  1. stimulus causes Na+ to flow in long enough to change potential to -55mV (known as threshold potential)
  2. when threshold potential is reached, voltage gated Na channels open and the charge changes to +30mV (known as depolarisation due to change from - to +)
  3. after depolarisation, there's a return to the resting potential, that happens through opening of K+ channels (this is repolarization, - potential is established)
  4. after repolarization, there;s an 'overshoot', where the potential dips to below -70mV (known as hyperpolarization)
  5. resting potential returned by Na/K pump
• Action potentials:

  A) resting

  B) positively

  C) depolarization

  D) repolarization

  E) resting potential

  F) depolarization

  G) repolarization

  H) hyperpolarization

  I) resting potential

  J) Na+

  K) K+

  
• Impulse conduction part 1

  • An action potential at the trigger zone of an axon causes an electric current to flow to the adjacent region of the axon membrane
  • Local current stimulates the adjacent axon membrane to the threshold and causes another action potential
  • In turn the new action potential stimulates the next region and this pattern repeats as a series of action potentials
  • This is called impulse conduction
• Impulse conduction summary:

  1. neuron membrane maintains resting potential
  2. threshold stimulus is recieved
  3. sodium channels in the trigger zone of the axon open
  4. Na+ diffuse inwards, depolarizing the axon membrane
  5. Potassium channels in the axon membrane open
  6. K+ ions diffuse outward, repolarizing the axon membrane
  7. the resulting action potential causes a local eletric current that stimulates the adjacent portions of the axon membrane
  8. a series of action potentials occur along the axon
• Impulse conduction part 2:

  • unmyelinated axon
  • continuous conduction - = movement of an action potential along an unmyelinated axon
  • Flows uninterrupted along the entire length of the axon
  • Myelinated axon
  • Myelin insulates and prevents the ion movement through the whole axon
  • Myelin sheath would prevent impulse conduction altogether however nodes of Ranvier interrupt the sheath
  • Thus action potentials only occur that these nodes and jumps from node to node
  • This is known as saltatory conduction

  
• Impulse conduction part 3:

  • Speed of the impulse depends on the diameter of the axon
  • Greater diameter = faster impulse
  • the impulses along a mylinated neuron are alot faster than those across an unmylinated neuron
  • Refractory period
  • Follows an action potential, the threshold stimulus wont trigger another action potential at that part of the axon
  • This ensures that the impulses only happen in one direction along the axon and also limit the frequency of action potentials
• Synapse = the functional connection between two neurons

  • Neurons at the synapse arent in direct contact they are separated by the synaptic cleft
  • Presynaptic neuron = neuron conducting the impulse to the synapse
  • Postsynaptic neuron = neuron receiving the impulse at the synapse
  • Synaptic transmission = mechanism in which the impulse travels across the synaptic cleft
  • Neurotransmitters = chemicals that are released by the neuron that carry out synaptic transmission
  • These bind to receptors on the postsynaptic
  • Effect is either excitatory (stimulate impulse) or inhibitory (prevent impulse)
• The synapse:

  A) presynaptic

  B) mitochondrion

  C) postsynaptic

  D) neurotransmitter

  E) synaptic cleft

  F) knob

  G) vesicles

  H) cleft

  I) receptors

  J) synapse

  K) synaptic cleft

  
• Synaptic transmission:

  • Excitatory and inhibitory actions:
  • Inhibitory
  • Stimulus will cause Cl- ions to flow in or K+ ions to flow out and this makes the charge more negative (neuron less likely to get excited)
  • Overall effect on the post synaptic neuron depends on the neurotransmitters released

  A) excitation

  B) inhibition

  C) inhibitory

  D) excitatory

  
• Types of neurotransmitters:

  A) acetylcholine

  B) monoamines

  C) amino acids

  D) neuropeptides

  E) gases

  
• Events leading to the release of a neurotransmitter

  • action potential passes along axon and over surface of synaptic knob
  • synaptic knob membrane becomes more permeable to calcium ions and they diffuse inwards
  • in presence of calcium ions, synaptic vesicles fuse to synaptic knob membrane
  • synaptic vesicles release neurotransmitter (Nt) into synaptic cleft
• Synaptic transmission part 2:

  • When an action potential reaches the synaptic knob, the membranes permeability to calcium ions increases
  • Calcium ions diffuse inward and fuse with some vesicles that releases their contents
  • Neurotransmitters (Nt) are then released across the synaptic cleft and bind to the receptors on the postsynaptic
  • released Nt is removed or decomposed from the synaptic cleft to prevent the Nt from acting on the postsynaptic neurons continuously
  • Some decomposed by enzymes
  • Others are transported back into synaptic knob that releases them or into nearby neurons or neuroglia
• Impulse processing part 1

  Neuronal pools:

  • Neurons in the CNS are organised into neuronal pools
  • groups of neurons that make hundreds of synaptic connections with each other and perform a common function
  • Each pool receives an input and generates an output
  • Neuronal pools maybe have excitatory or inhibitory effects on other pools/ peripheral effectors

  Facilitation:

  • repeated impulses on an excitatory presynaptic neuron that may cause that neuron to release more neurotransmitters in response to a single impulse, which makes it more likely to bring the postsynaptic neuron to its threshold
• Impulse processing part 2

  Convergence:

  • 2 or more presynaptic neurons forming synapses with the same postsynaptic neuron
  • This makes it possible for impulses arriving from different sources to have an additive effect on a neuron
  • Also allows the nervous system to collect a variety of info, process it and respond to it in a specific way

  Divergence:

  • A single presynaptic neuron forming synapses with two or more postsynaptic neurons
  • In the process, the spread of an impulse from one neuron to several others allows amplification of the effects of the impulse

  
• Types of nerves:

  • Nerves = bundles of axons located in PNS
  • Sensory nerves = conduct impulses to brain or spinal cord
  • Motor nerves = conduct impulses to muscles or glands
  • Mixed nerves = include axons of both sensory and motor nerves
  • Axon is referred to as nerve fibre
  • Sensory fibers/ afferent fibers = axons that bring sensory information into the CNS
  • Motor fibers/efferent fibers = conduct impulse

  A) nerve

  B) perineurium

  C) endoneurium

  D) myelin

  E) fascicles

  
• Reflex arc:

  • Begin with a receptor and leads to the CNS, which then connects to the effectors via the motor neuron

  A) internal

  B) external

  C) receptor

  D) brain

  E) sensory

  F) motor

  G) brain

  H) spinal cord

  I) effector

  J) stimulation

  K) muscle

  L) gland

  
• Reflex behaviour

  • They are automatic responses to stimuli
  • They help to maintain homeostasis
  • Example is the patellar reflex
  • Strike the patellar ligament just below the patellar to initiate a reflex
  • The muscle group attached to the patella tendon is pulled slightly and it stimulates a stretch in these muscles
  • The receptors pass along the impulses to the spinal cord and that triggers to the effector and as a result the muscle group contracts in response

  
• Reflex behaviour part 2:

  Examples is the withdrawal reflex

  • Happens when a person unexpectedly touches a body part to something painful
  • This activates skin receptors and sends sensory impulses to the spinal cord
  • The impulses pass to the interneurons towards motor neurons that activates the muscle fibres that cause the body part to withdraw

  
• Meninges part 1:

  • Bones, membranes and fluid surround the CNS organs
  • Brain = cranial cavity
  • Spinal cord = vertebral column
  • Meninges refers to the 3 layers of membrane that cover the brain and the spinal cord
  • dura mater
  • arachnoid matter
  • pia mater

  A) scalp

  B) cranium

  C) cerebrum

  D) vertebra

  E) spinal cord

  F) meninges

  G) dura mater

  H) arachnoid mater

  I) pia mater

  J) cerebrum

  
• Meninges part 2:

  • dura mater
  • outermost layer
  • composed of tough white fibrous connective tissue that contains many blood vessels and nerves
  • In some regions it extends inward between the lobes of the brain
  • Arachnoid mater
  • Thin membrane without blood vessels that lies between the dura and pia maters
  • Subarachnoid space contains the clear cerebrospinal fluid
  • Pia mater
  • Very think and contains many nerves and blood vessels that nourish the underlying cells of the brain and spinal cord
  • Layer hugs the surface of the organs
• The meninges:

  A) spinal cord

  B) pia mater

  C) arachnoid mater

  D) dura mater

  E) spinal nerve

  F) central canal

  G) vertebra

  H) anterior

  I) posterior

  J) spinal nerve

  
• Spinal cord = slender column of nervous tissue that passes downward from the brain into the vertebral canal

  A) cervical enlargement

  B) spinal cord

  C) vertebral cana