Nervous system

stem

  • Brain + spinal chord = Central Nervous System

  • Peripheral Nervous System has 2 sections

    • Cranial and spinal nerves

    • Skeletal/voluntary muscles

  • Autonomic Nervous system

    • Automatic functions

Cranial and spinal nerves

  • Note that cranial nerves
    do not originate from the spine

  • Emerge directly from the brain at
    irregular intervals/locations

  • Largely due to their functions

  • Includes the brainstem

  • Dorsal view of brain showing
    origins of cranial nerves

    • Note their irregularity

    • Bilateral symmetry –
      one on each side.

  • Cranial nerves

    • Attached to base of brain

    • Convey sensory information

    • Conveys message to muscles and glands

  • Spinal nerves

    • Emerge at regular intervals from segments of spinal cord

    • Sensory information from the rest of the body reaches the spinal cord through the spinal nerves

    • Sends messages to brain from

      • Muscles

      • Sensory organs

      • Viscera

      • Sub-cutaneous and deep tissue

  • Body also talks to brain via cranial and spinal nerves

Nerves & The PNS

Nerves

  • Nerves are a collection of nerves fibres

  • These fibres transmit info to and from the CNS

  • Come in three types/classes

    • Class A- Relates to muscle and tendon movement

    • Class B covers involuntary impulses like digestion and lung movement

    • Class C is responsible for pain and temperature sensations

Class A nerves (muscle/Tendon)

  • Typically largest class in number

  • Thickest class (1/5 of human hair)

  • Usually transmit rapidly

  • Most are myelinated- meaning they are covered in a myelin sheath- promotes rapid transmission

    • Myelin structure: plasma membrane; surrounds the nerve fibre

    • Myelin function: protects; promotes rapid transmition

    • Myelin Sheath Normal nerve Damaged myelin sheath Exposed nerve fiber Nerve affected by MS

Class B nerves (involuntary impulses)

  • Involuntary impulses

    • Digestion, breathing, blinking

    • Pupil dilation, perspiration

  • Think about exercising

    • Increased HR and sweating, breathing- none of this is consciously manipulated

  • Myelinated but thinner than Class A nerves

    • Meaning they are slightly slower

    • Think about their function- they don't need to be fast

Class C nerves (pain, temp)

  • Generally unmyelinated, thin

    • Pro: they can reach all parts of the body equally

    • Con: they are the slowest

      • Travel at around 7inches/second compared to class A 299feet/sec

  • Nerve signals are known as action potentials

The Central Nervous System (CNS)

  • CNS communicates with the rest of the body via PNS

 

The Brain

  • Consists of 3 major parts

  • Brain stem

  • Cerebellum

  • The cerebral hemispheres (aka cerebrum or cortex)

cerebrum brain stem cerebellum

  • Brain stem

    • A “primitive” brain region

    • Meaning the earliest to evolve

    • Humans share similar neuroanatomy with most animal species

    • With basic functions

    • Control physiological functions

    • Automatic behaviours
      (e.g. breathing, heartbeat, blood pressure)

    • Made of the midbrain, pons and medulla

  • The Cerebellum

    • Control and coordinate movements

    • Scalp Skull Periosteal dura mater Meningeal dura mater Arachnoid mater Subarachnoid space Pia mater Cerebral cortex

    • Balance & Posture

    • Coordination of voluntary movements

    • Motor Learning

    • Cognitive Functions

    • Involved when we play the piano, practice ballet, ride a bike

    • Problems with the cerebellum?

      • Slowing of voluntary movement, tremor, poor/absent reflexes, weakness/lack of energy, loss of coordination, balance, speech....

  • Protecting the CNS

  • Scalp Skull Periosteal dura mater Meningeal dura mater Arachnoid mater Subarachnoid space Pia mater Cerebral cortex

The blood-brain barrier

  • Protects the brain from chemical assailants

    • toxins, hormones, neurotransmitters (in rest of body)

  • Formed by very tight capillaries (blood vessels)

  • Cells connected with tight junctions

  • Fewer substances can travel from the blood (inside the capillaries) into the brain

  • Esp. toxins, which might damage neurons

  • Not foolproof -- many poisons and drugs can affect the brain

  • Foundation of understanding how antidepressants and other drugs get into the brain