The Nervous System

Because the brain and nervous system are delicate, the have protection from different layers.  The first layer is bone; cranial bones encase the brain, vertebrae for the spinal cord.

The inner layer of the central nervous system is the meninges which in turn have three membranes:

  • Dura Mater – The strong white fibrous outer layer
  • Arachnoid Membrane – a delicate fine webby centre layer
  • Pia Mater – clear transparent layer that adheres to the outer surface of the brain and spinal cord and contains blood vessels.

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The Autonomous Nervous System is part of the peripheral nervous system and regulates the functions of our internal organs, for example the heart, lungs  and stomach.  It controls some of the smooth and caridac muscles and glands of our body.  We are often unaware of the Autonomous nervous system because it offers involuntary and reflexive actions such as blood vessel dilation or faster heart beats.

runner sleeper

http://faculty.washington.edu/chudler/auto.html

 

  • In emergencies that cause stress and require us to “fight” or take “flight” (run away)
  • In nonemergencies that allow us to “rest” and “digest.”

The ANS is divided into three parts:

  • The sympathetic nervous system
  • The parasympathetic nervous system
  • The enteric nervous system

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  • Sympathetic Nervous system is part of the Autonomous nervous system and prepares the body to deal with immediate threats to the internal environment, producing the fight or flight response.
  • Parasympathetic nervous system is also part of the autonomic nervous system and coordinates the body’s normal resting activities – sometimes called the ‘rest and repair’ division
  • Enteric nervous system is a network of nerve fibres that innervate the viscera (gastrointestinal tract, pancreas, and gall bladder).

Divisions of the brain stem and their function

The brain stem, like the spinal cord performs sensory, motor and reflex functions.

The Midbrain

Contains reflex centres for certain cranial nerve reflexes; for example pupillary reflexes and eye movements, mediated by the 3rd and 4th cranial nerves.

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The Pons

Contains centres for reflexes mediated by the 5th, 6th, 7th and 8th cranial nerves, which also control eye movements.  In addition the pons contains the pneumatic centres that help to regulate respiration.

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The Medulla Oblongata

Nucleii in the medulla contain a number of reflex centres.  Of first importance are the cardiac vasometer and respiratory centres; also non-vital reflexes such as coughing, vomiting, sneezing, swallowing and hiccuping.

The anatomy and function of the cerebellum, di-encephalon and cerebrum

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Cerebrum

  • This is the largest and uppermost division of the brain
  • It has two halves; the left and right cerebral hemispheres.
  • It is covered with a cerebral cortex, which has a thin surface yet contains 6 layers;each composed of millions of axon terminals synapsing with millions of dendrites and cell bodies of other neurons.

Function of cerebrum

cerebral cortex structure

http://www.tutorvista.com/content/biology/biology-ii/control-and-coordination/central-nervous-system.php

  • somatic senses such as touch, temperature and pressure
  • somatic sensory map of the body
  • motor functions
  • emotions, memory and consciousness functions

Beneath the cerebral cortex lies the large interior of the cerebrum.  It composed mostly of white matter (axons), which contains islands of grey matter(cell bodies), that contain cerebral nucleii.

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Structure of the Diencephalon

human brain diagam with labels

http://www.tutorvista.com/content/biology/biology-ii/control-and-coordination/central-nervous-system.php

Located between the cerebrum and the midbrain.  It consists of:

  • The Thalamus -sensations, emotions, arousal
  • The Hypothalamus, survival, enjoyment, links mind and body, links the endocrine system and the nervous system, regulates appetite and body temperature, arousal
  • Optic chaisma
  • Pineal body – body clock rhythms and secretin of melatonin
  • Others

Structure of the Cerebellum

  • 2nd largest part of brain
  • grey matter makes up cortex
  • white matter makes up the interior – arbor vitae – a distinctive vein-like pattern

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  • has numerous sulci and gyri

Functions

3 general functions all have to do with control of skeletal muscles.:

  • skilled movementscoordinates the activities of groups of muscles
  • balance
  • posture – movements are efficient and coordinated.

 Qualities that define a neuron

Excitable cells that initiate and conduct impulses that make possible all nervous system functions

Make up only around 10% nerve cells

Main component of a neuron is a rather large cell body with at least 2 processes:

One of these will be the efferent axon, transmitting information away from the cell body, whilst the other will be the dendrite, normally more than one and with the appearance of tree branches.

Dendrites transmit incoming sensory information to the cell body

Both afferent sensory dendrites and efferent axons are known collectively as nerve fibres.  only the axons are myelinated, not the sensory dendrites.

Neurons can be classified functionally depending on the direction that they conduct impulses:

afferent neurons:transmit towards the brain or spinal cord

inter neurons; found only in brain and spinal cord – conduct impulses from afferent neurons to motor neurons.

efferent (motor) neurons; conduct impulses towards muscles or glands, away from brain/spinal cord.

The Neuron

cnx.org

Is similar to many cells, with all the normal components of a typical cell that you would expect.  However extending through the axon’s body are numerous neurophils, bundles of neurofilaments.  the axons can vary in length, may be as long as a meter and may have many branches.  the extended plasma membrane encases the many neurofibrils.  It is through The plasma membrane that the electrical nerve impulses pass.

Also contained within the neurons are microtubules and even smaller microfilments – all of these provide a network for transporting important molecules to and from the far end of the neuron.  These many tubules all ultimately lead to the end of the axon called the synaptic knob.

It is at this synaptic knob that the electrical impulses received cause chemical compounds called neurotransmitters to be released from the numerous small sacs/ vesicles which then cross the very narrow synaptic cleft and connect onto the post synaptic membrane of the new neuron.

cla.calpoly.edu

 

5 Types Glia and their functions

cnx.org

Astrocytes are star shaped – the largest and most numerous of the glia.  They form tight sheaths around brain capillaries which, with tight junctions between capillary endothelial cells, constitute the blood brain barrier.

Microglia are small usually stationary cells, in inflammed brain tissue they enlarge, move about and carry on phagoocytosis.

Epyndymal cells resemble epithelial cells and form thin sheets that line fluid filled cavities in the CNS – some produce fluid, others aid in the circulation of fluid.

Ogliodendrocytes smaller than astrocytes, with fewer processes, hold nerve fibres together and produce the myelin sheath

 

Schwann Cells are found only in the peripheral nervous system, they support nerve fibres and form myelin sheaths.  Gaps in the myelin sheath are called nodes of Ranvier.  Sattelite cells are schwann cells that cover and support cell bodies in the PNS

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