Gr12 Nervous System

• the cerebellum coordinates muscle activity to maintain balance and posture.
• / the brain is divided into two hemispheres
• the brainstem is the most primitive part of the brain, it controls vital functions such as breathing, heart rate, blood pressure, swallowing, digestion, sleep, and wakefulness
• The nervous system is the body's control and communication centre and ensures that humans respond effectively and quickly to their environment.  This ensures their survival.
• Stimulus:  A physical or chemical change in the environment that requires a response from the organism.
• Meninges:  The three protective membranes that surround the brain and spinal cord.
• Reflex action: A quick, involuntary, automatic action that involves the spinal cord and does NOT involve the brain.
• Reflex arc:  The pathway a reflex action follows in order to bring about a reflex action
• Synapse:  A gap between two consecutive neurons or between a neuron and an effector.
• Neurotransmitter:  A chemical substance that enable an electrical impulse to flow smoothly between consecutive neurons.  (eg. Acetylcholine)
• Receptor:  an organ that detects the stimulus and converts it into an impulse
• Effector:  an organ or gland that receives the impulse from the CNS and carries out the appropriate response
• The nervous system is divided into two parts:

  1.  The Central Nervous System (CNS)

  2.  The Peripheral Nervous System (PNS)
• The central nervous system is made up of two parts:

  1.  The brain

  2.  The Spinal Cord
• The brain is the enlarged upper part of the spinal cord, protected by a bony cranium, cerebrospinal fluid and three membranes called meninges.

  These meninges are:

  The dura mater - outermost membrane

  The arachnoid mater - middle membrane

  The pia mater - the membrane closest to the brain
• Label this diagram

  A) Cerebrum

  B) Medulla Oblongata

  C) Spinal Cord

  D) Cerebellum

  E) Corpus Callosum

  
• Cerebrum: controls voluntary actions;

                           receives and interprets sensations;

                           responsible for higher mental functions eg. memory, intelligence,  judgement.
• Corpus callosum:  a white band of neurons that connect the two hemispheres of the cerebrum.
•  Cerebellum (tree of life): controls all voluntary actions to ensure smooth movement;

  controls muscle tone to maintain balance and posture.
•  Medulla oblongata (part of the brain stem):  controls involuntary functions eg. breathing, blood pressure, peristalsis. 
• The spinal cord consists of:

  A central canal that runs through the centre of the spinal cord, and is filled with cerebrospinal fluid.
• The "grey matter" forms the letter H on the inside and the "white matter " is located on the outside of the letter H.  It contains myelinated nerve fibres that extend to and from the brain.

  A) Gray Matter

  B) White matter

  
• Each spinal nerve has a dorsal root made up of sensory neurons, that conducts impulses from the receptors to the grey matter of the spinal cord.
• Each spinal nerve also has a ventral root made up of motor neurons, that conducts impulses from the grey matter of the spinal cord towards the effector.
• The cells bodies of the sensory neurons occur in the swelling of the dorsal root.  This swelling is called a ganglion.
• The spinal cord is protected by the same three meninges that protect the brain.

  True or False?

  True
• The two main functions of the spinal cord are:

  • Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions.
  • Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as sensations of touch, pressure, and pain.
• Cranial nerves are connected to the brain and conduct impulses to and from the sensory receptors and muscles in the face.
• Spinal nerves enter and leave the spinal cord between the vertebrae.
• The functions of the PNS are therefore twofold:

  1.  Sensory function:  conducts impulses from the receptor cells in the sense organs to the CNS.

  2.  Motor function:  conducts impulses from the CNS to the effectors (muscles or glands).
• PNS


  All the nervous tissue outside of the CNS that links the CNS to the receptors or effectors of the body
• Cranial nerves


  • Connected to the brain and conduct impulses to and from the sensory receptors and muscles in the face
• Spinal nerves


  • Enter and leave the spinal cord between the vertebrae
• Functions of the PNS

  • Sensory function: conducts impulses from the receptor cells in the sense organs to the CNS
  • Motor function: conducts impulses from the CNS to the effectors (muscles or glands)
• Somatic nervous system


  Motor neurons conduct impulses from the CNS to skeletal muscles that control voluntary movements
• Autonomic nervous system


  Motor neurons conduct impulses from the CNS to cardiac and smooth muscles and glands, that control involuntary movements
• Sympathetic nervous system - prepares the body for "fight or flight".
• Parasympathetic nervous system - return the body to normal after being stimulated by the sympathetic nervous system.
• There are three types of neurons:

  1.  Sensory/Afferent neuron

  2.  Motor/Efferent neuron

  3.  Interneuron/Connector neuron
• A reflex is a quick, automatic response that involves the spinal cord and not the brain.