Post on 20-Jan-2017
Unit 10 - The Nervous SystemCNS, PNS, and associated components
The Big PictureNervous system is divided into two main categories:
Central Nervous system (CNS): Brain and Spinal Chord
Peripheral Nervous system (PNS): Nerves to/from CNS
PNS is further divided into:
Somatic (SoNS): Connects the CNS to voluntary muscles
Autonomic (ANS): Regulates involuntary body functions
Big Picture Cont.Autonomic is further divided into:
Sympathetic (SNS): “fight or flight”
Parasympathetic (PSNS): “rest and digest”
Nervous System Flow Chart
CNSParts and Functions
The BrainThe main components of the brain include:
cerebrumcorpus callosumcerebellumthalamushypothalamuspituitary glandmedulla oblongatameninges
Cerebrum
Cerebrum ANATOMY
2 hemispheres
4 lobes (Frontal, Parietal, Occipital, Parietal) separated by sulci.
Cerebrum PHYSIOLOGY
Two hemispheres:
Right: creativity
Left: logic
Connected by the corpus callosum
CC is associated with integration of motor, sensory, and cognitive functions between the hemispheres.
Cerebrum PHYSIOLOGY
Sulci differentiate the cerebrum into 4 lobes
Frontal Lobe: Reasoning, Movement, Problem Solving
Parietal Lobe: Perception, Orientation, Recognition
Occipital Lobe: Visual processing
Temporal Lobe: Auditory stimuli, Speech, Memory
Cerebellum ANATOMY
“Little Brain”
Two hemispheres with a highly folded surface.
Cerebellum PHYSIOLOGY
Regulate eye movements
Coordinate limb movements
Maintain posture and balance
Motor decision making
ThalamusRelays sensory information from the body to the cerebral cortex.
HypothalamusInvolved in: homeostasis, emotion, thirst, hunger, circadian rhythms, and control of the autonomic nervous system.
Control of the pituitary gland
Pituitary Gland
“Master Gland” of the endocrine system
Under control of the hypothalamus
Pituitary Gland
Medulla Oblongata
Medulla OblongataControls involuntary functions such as:
Respiration
Heart Rate
Digestion
Relays higher level brain centers with the spinal chord.
Meninges
3 Layers
Dura Mater: outer layer closest to skullArachnoid Mater: provides cushioning effect for CNSPia Mater: attached to brain, contains capillaries
Subdural haematoma (btwn dura and arachnoid) resulting from traumatic event causes bleeding and inter cranial pressure and brain trauma
Remember...
The Peripheral Nervous System is composed of:
Sensory Neurons (Afferent Neurons)
Motor Neurons (Efferent Neurons)
What are these made of and how do they transport signals?
Parts of Neurons
Receive signals from other nerve cells
Covered in synapses
Parts of Neurons
Conveys electrical signals (range from 0.1mm to 2m)
Point of contact w/ cell body = Axon Hillock
Parts of Neurons
Carry out basic life functions of the neuron, including production of proteins and ATP.
Parts of Neurons
Protective covering of long Axons
Gaps btwn Schwann Cells are called Nodes of Ranvier
Sensory (Afferent) Neuron
Take information from sensory receptors to the CNS
Chemoreceptors are specific to the function they perform (taste, pain, etc.)
InterneuronAct as middle men between sensory and motor neurons
Reside completely within the CNS
Have many varieties and are multipolar (more than one dendrite)
Motor (Efferent) Neuron
Carry signals from CNS to effectors
Effectors can be glands or muscles as examples.
Signal Generation
Electrical activity is due to movement of ions past the cell membrane (Na+ and K+)
Neurons have an Electrical Charge Different from the Extracellular Fluid that surrounds them. A difference in electrical Charge between Two Locations is called a POTENTIAL
Signal Generation RESTING POTENTIAL
Positively charged Na+ pumped out of cell, K+ “leak” out passively.
Causes a negative charge inside cell
Cell is now polarized and maintains this situation until stimulated.
Signal Generation THRESHOLD
Stimulation of the nerve is required to begin an impulse down the nerve
One sufficient stimulation occurs we can say that a THRESHOLD has been met
Once an impulse begins it can not be stopped, hence an “all or none” system is employed by neurons.
Signal Generation ACTION POTENTIAL
Stimulation of the nerve causes gates in the neuron to open.
Gates allow positive ions (Na+) to enter neuron causing the neuron to DEPOLARIZE.
Signal Generation ACTION POTENTIAL
After the impulse passes K+ gates allow K+ to leave cell
This causes REPOLARIZATION of the neuron.
Signal Generation ACTION POTENTIAL
This depolarization and repolarization is what we call an action potential or nerve impulse.
Signal Generation ACTION POTENTIAL
Na+/K+ pumps now return the respective ions to the proper side of the cell membrane
This is called the REFRACTORY period
No nerve signal can propagate during this period.
Signal Propagation MYELINATION
Axons that are myelinated propagate signals faster
Signals jump between the myelination (nodes of ranvier)
Speeds of 200 m/s can occur
The Synapse
Axons ends are slightly swollen and are called AXON TERMINALS.
These terminals transmit signals with dendrites, effectors (muscles) or receptors (sensors).
Small vesicles at the axon terminals contain NEUROTRANSMITTERS.
The Synapse NEUROTRANSMITTERS
Chemicals that are released into the synapse
Ex: Acetylcholine (ACh)
Join to receptors on neuron receiving the impulse
Cause membrane to become permeable to Na+ and a depolarization of the neuron
Threshold is met, and a signal propagates along the neuron.
Acetylocholinesterase rapidly breaks down ACh so that the chemical signal stops
Reflex Arc
Reflex ArcSensory neurons are stimulated and send a signal to the spinal chord
Interneurons relay the stimuli to motor neurons
Motor neurons send the signal to the effector muscles
The Brain does not receive a signal before the movement occurs and pain is not sensed until after the effector has been stimulated
SYMPATHETIC
Fight or Flight
Increases HR
Inhibits digestion
Dilates pupils
Vasoconstriction
Increases respiration
PARASYMPATHETIC
Rest and Digest
Pupil constriction
Promotes digestion
Controls resting HR
Relaxes muscles
ANS BRANCHES