Nervous system : the basics

• What is the function of the Nervous sytem?

  High speed communication throughout body

  
  

  1) Sensation

  2) Integration

  3) Response
• What does sensation involve

  - sensory receptors that sense change from internal & external environment / stimuli

  - Take this in as sensory input

  ex: speed, vision
• What does integration involve

  -Processing and interpreting sensory input

  -Make a decision : unconscious and conscious
• What is Response ?

  Motor output

  -Send signals to effector organs to carry out a response from stimuli

  
  

  Muscle or glands
• Describe the process all together: Hiking example from lecture


  We go hiking we SEE a branch we then INTEGRATE sensory input which will determine speed and where you are going, You then make DESCION to duck down , You will then send out motor signal to RESPOND
• What are the 2 basic divisions of the Nervous system? What do they involve?

  1) Central nervous system (CNS)- majority of integration occurs here

  - brain

  - spinal cord

  
  

  2) Peripheral nervous system (PNS)

  - cranial nerves --> from brain

  - spinal nerves--> from spinal cord

  - ganglia
• What are Ganglia ?


  areas outside of CNS that are concentrations of neuron cell bodies/ neursoma
• What are the functional organizational divisions of the Peripheral nervous system?

  Directions of signals

  
  

  1) Sensory/ afferent - signals going towards CNS

  2) Motor./efferent- leaving the CNS to an effector organ

  - Motor output

  
  

  Regions

  1) Somatic: structures external to thoracic/ abdominal cavities

  - muscle, bone, skin

  2) Visceral: to internal organs

  - digestive tract, urinary tract , etc
• What are effector organs?

  muscle, gland, organ that carries out response
• What are the 4 subdivisions of the PNS?

  1) Somatic sensory: bringing in sensory input from outer walls

  - feeling things, temp, pressure

  
  

  2) Visceral sensory - sensory input from organs

  - stretch , internal temp, chemical changes

  
  

  3) Somatic motor- responses going to outer body wall

  - carry sensory input to skeletal muscles

  
  

  4) Autonomic NS/ Visceral motor : carrying response/ motor output to organs

  ex: heart, digestive tract, glands

  - sympathetic : flight or fight

  - Parasympathetic : rest & digest
• A nerve that conducts impulses from the CNS to Cardiac muscle would be considered part of which subdivision of the nervous system?

  Visceral motor
• What is a nerve impulse/ action potential?

  a reversal of electrical charge that travels along the membrane of a neuron

  there's a change in the electrical charges across the membrane
• What is involved in the Nervous Tissue ?

  1) Neurons

  2) glial cells/ neuroglia
• What are Nuerons ?

  *Highly specialized cells to conduct nerve impulses

  - transmitted along neurilemma/ neuron membrane
• Characteristics of neurons


  1) Excitable : respond to stimuli

  
  

  2) Conductivity : conduct electrical signal

  
  

  3) Secretion : secrete neurotransmitter

  - chemical signals that tells next neuron to continue signal

  
  

  4) long lived, DO NOT DIVIDE!!!! --> can not be replaced

  
  

  5) high metabolic rate: consume a lot of ATP
• Describe the structure of neurons : cell body

  Neurosoma = cell body

  Nucleus

  Cytoplasm, organelles,

  
  

  Most neurosoma are in the central nervous system

  Some will be in clusters outside the CNS so in the Peripheral nervous system
• Describe the Processes of the neurons : Dendrites

  Dendrites: RECEIVERS

  receive signals from many neurons and carry signal to neuron cell body

  - Have a high surface area with its many branches

  small branchlike
• Describe the Processes of the neurons: Axons


  SENDERS !!!!

  carries signals away from cell body

  contains....

  AXON HILLOCK

  - trigger zone , triggers signal to go out from the cell body

  some will have

  AXON COLLATERALS , not all

  
  

  TERMINAL ABORIZATION

  - small little branching at end of axon

  
  

  TERMINAL BOUTONS/ axon terminals

  - button like

  - signal to dendrites of next neuron or effector organ
• What happens once the signal reaches the terminal bouton of the axon?

  We have a SYNAPSE = specialized cell junctions

  
  

  consists of....

  presynaptic neuron= the one carrying the signal

  Postsynaptic neuron = nueron that recieves the signal

  
  

  terminal bouton will be filled with sacs aka synaptic vesicles containing neurotransmitters

  
  

  Synaptic cleft = a gap
• What happens at a synapse?

  -As action potential reaches the terminal bouton

  
  

  - that signals the synaptic vesicles to release neurotransmitters into the synaptic cleft

  
  

  -the postsynaptic neuron will have receptors that bind to the neurotransmitters

  
  

  -this fires an action potential which

  
  

  -allows the signal to continue throughout the neurons
• What types of signals do we have ?

  Electrical= signal within neuron

  - changes of charges within membrane

  
  

  Chemical = signal between neuron

  - neurotransmitters
• Give me the types/ Variety of neurons

  Multipolar = 2 or more processes

  1 axon , many dendrites

  - makes up 99% of neurons

  
  

  Bipolar= 2 processes

  - 1 axon & 1 dendrite

  - rare

  - sensory neurons ---> retina , nasal mucosa, inner ear

  
  

  Unipolar= single process leaves neuron cell body

  - rare

  - PNS, sensory ganglia

  
• Types of neurons by Function

  Sensory neurons - afferent

  - take signals toward CNS

  
  

  Interneurons

  - located in CNS ONLY!!

  - receive info from sensory neurons & integrate/process

  -90% of neurons

  
  

  Motor neurons

  -carrying response to effector organ
• A nerve that conducts impulses from your infraspinatus to the central nervous system would be considered part of which subdivision of the nervous system?

  Somatic sensory
• Neuron process that carry signals toward the neurosoma are

  Dendrites!!!!!
• What are Neuroglia?


  Supportive cells

  Functions

  1. support neurons --> structural , providing a good envior.

  2. Cover non synaptic parts

  -will cover large portions of the neuron

  6 types

  - 4 in CNS

  - 2 in PNS
• What are the Neuroglia in the CNS?

  1. Astrocytes

  2. Microglial

  3. Ependymal cells

  4. Oligodendrocytes
• Astrocytes


  Most abundant!

  - looks like a star

  - have processes radiating from body

  
  

  Functions:

  - big supporters

  - control ionic envior.

  - nourish

  - communicate

  
  

  Covers brain surface, nonsynaptic & gray matter of CNS
• Microglial cells


  Small elongated macrophages

  
  

  Function : phagocytosis, removing debris and pathogens
• Ependymal cells

  resemble epithelial cells

  - line ventricles of brain and central canal of spinal cord

  
  

  Function: production & circulation of cerebrospinal fluid

  cete rebral spinal fluid= acts as a cushion, float in CNS, circulate nutrients, help remove waste
• What does cerebrospinal fluid do ?


  acts as a cushion, float in CNS, circulate nutrients, help remove waste
• Oligodendrocytes


  cell body with many arm-like processes

  - reach out and wrap around portion of axon

  creates--> myelin sheath

  Function: myelination ---> helps insulate so electrical signals do go out of neuron
• The type of neuroglial cells responsible for producing and circulating cerebrospinal fluid is

  Ependymal cells
• Neuroglia of the Peripheral nervous system

  1. satellite cells

  2. Schwann cells
• Satellite cells


  surround cell bodies

  functions:

  -support

  - help regulate envior.
• Schwann cells


  wrap around axon like pig in a blanket

  - each cell forms a segment of myelin sheath

  Function : Insulation
• what are myelin sheaths

  In CNS made by = oligodendrocytes

  In PNS made by = schwann cells

  - cover over an axon

  
  

  Myelin = plasma membrane

  -made of water, lipids, proteins

  
  

  process= myelination
• Node of Ranvier


  myelin sheath gap , internodal segments
• Myelin functions


  1. Insulation

  
  

  2. Energy efficient propagation

  - better signaling with less energy

  
  

  3. Speed of conduction

  depends on

  -diameter of nerve fiber ---> bigger diameter= faster

  - myelin= carries signal faster

  aka saltatory propogation

  jumps from gap to gap ----> so much faster than walking 🚶‍♀️
• What is Gray matter

  Unmyelinated neurons

  composed of

  - cell bodies, dendrites, interneurons, motor cell bodies