Anatomy and Physiology I

• Nervous System


  Master controller and communicating system of the body
• Nervous System


  • Responses are rapid and specific
  • Responses can be electrical or chemical
  • Enables human ability to interact with and respond to environment
• Functions of the Nervous System

  1. Sensory input

  2. Integration

  3. Motor output

  
• PNS


  • Outside the CNS
  • Peripheral nerves communicate with CNS
  • 2 divisions: sensory & motor
  • Somatic: skin, skeletal muscles, voluntary control
  • Autonomic: smooth muscle, digestive, cardiac, involuntary control
• CNS


  • Brain & Spinal Cord
  • Control center
  • Interprets sensory information and decides on motor output
  • Information from reflexes, experiences, external environment

  
• Nervous Tissue


  • Neurons (nerve cells)
  • Neuroglia (support cells)

  
• Neurons


  • Structural and functional unit
  • Relay messages
  • Longevity
  • High metabolic rate, require glucose and O2
  • Amitotic - unable to divide
• Astrocytes


  • Most abundant, star-shaped
  • Radiating processes anchor neurons to capillaries
  • Determine capillary permeability
  • Guide formation of synapses between neurons
  • Recapture released neurotransmitters

  
• Microglia


  • Defense cells in the CNS
  • Long thorny processes monitor health of nearby neurons
  • Migrate toward injured neurons
  • Transform into specialised macrophage to phagocytose microorganisms
• Ependymal Cells


  • Line the central cavities of the brain and spinal cord
  • Form a permeable barrier between cerebrospinal fluid (CSF) and tissue fluid around cells
  • Cilia help circulate CSF

  
• Oligodendrocytes


  • Form protective and insulating myelin sheath around thicker nerve fibres in CNS
  • Destroyed in Multiple Sclerosis
• Satellite Cells


  • Surround the cell bodies of neurons in PNS
  • Support cells
  • Similar functions to astrocytes in CNS
• Schwann Cells


  • Surround all thicker nerve fibres in the PNS
  • Produce myelin sheath
  • Act like oligodendrocytes (CNS only)
  • Regeneration of damaged peripheral nerves

  
• Regeneration of damaged neurons

  • Only in PNS (Schwann cells actively repair)
  • Not in CNS (Oligodendrocytes and astrocytes inhibit axon repair)
• Overview of neuroglia


  • CNS: Astrocyte, Microglia, Ependymal cells, Oligodendrocytes
  • PNS: Schwann cells, Satellite cells

  
• Chemical synapses


  • Most common type of synapse
  • Release and reception of chemical messengers called neurotransmitters (NT's)
  • A pre-synaptic neuron is separated from a post-synaptic neuron by a synaptic cleft
  • NT's are stored in pre-synaptic neuron and released into synaptic cleft
  • NT's bind to specific receptor on post-synaptic neuron to exert an effect
  • NT's diffuse away from the synaptic cleft
  • NT's are degraded by enzymes after binding with receptor
  • NT's taken back up by pre-synaptic neuron
• Classification of Neurotransmitters


  • Acetylcholine
  • Biogenic amines (Noradrenaline, Dopamine, Serotonin, Histamine)
  • Amino acids (GABA, Glutamate)
  • Peptides (Endorphins)
• Acetylcholine (ACh)


  • First identified at neuromuscular junction
  • Botulinum toxin prevents ACh release = paralysis
  • Anti-acetylcholinesterases (insecticide poisoning) = sustained paralysis
• Biogenic amines


  • Broadly distributed in brain, roles in mood & appetite
  • Catecholamines (Noradrenaline, Adrenaline, Dopamine)
  • Dopamine: Parkinson's Disease = deficiency, Schizophrenia = excess, Cocaine blocks reuptake
  • Serotonin/Noradrenaline: Antidepressants SNRIs block reuptake
• Amino acids


  Gamma-aminobutyric Acid (GABA): inhibitory (amplified by drug/alcohol)
• Peptides


  • Pain signals, natural opiates (reduce perception of pain), generally inhibitory
  • Endorphins: natural feel-good or "runners high" feeling in athletes
• Central Nervous System


  Brain + spinal cord

  
• 4 regions of the brain

  • Cerebral hemispheres
  • Diencephalon
  • Brainstem
  • Cerebellum
• Grey matter


  • Neuronal cell bodies (in the brain = cerebral cortex + basal nuclei)
• White matter


  • Mostly myelinated neurons forming tracts
• Ventricular system of the brain

  • Lateral ventricles x 2
  • Third ventricle
  • Fourth ventricle
• Cerebrospinal fluid


  Function, production and location
• The lateral ventricles are connected by the septum pellucidum
• The cerebral hemispheres are separated by the longitudinal fissure
• The cerebral cortex contains grey matter
• The cerebral hemispheres contain five lobes: frontal, parietal, temporal, occipital, and insula
• The gyri and sulci increase the surface area of the cerebral cortex
• The blood-brain barrier is an almost impermeable membrane that separates the blood from the cerebrospinal fluid, protecting the brain from blood-borne compounds
• Central Nervous System: Brain Part B

  Functional regions of the cerebral hemispheres of the brain
• Cerebral hemispheres


  • Central sulcus
  • Precentral gyrus
  • Postcentral gyrus
  • Lateral sulcus
• Cerebral cortex


  • Composed of grey matter (cell bodies, dendrites, glia, blood vessels)
  • No fibre tracts
  • 40% of brain mass
  • Billions of neurons (arranged in 6 layers)
• Lobes of the cerebral cortex

  • Frontal (motor)
  • Parietal (sensory)
  • Occipital (visual)
  • Temporal (auditory)
  • Insula
• Cerebral cortex


  Conscious mind (sight, hearing, speaking, thinking)

  
• Frontal lobe - motor

  • Primary Motor Cortex (Precentral gyrus, controls simple motor tasks, voluntary movement of skeletal muscles)
  • Premotor Cortex (Anterior to primary motor cortex, more complex or learned motor tasks)
  • Prefrontal Cortex (Large anterior region, task management, working memory, inhibition, planning and decision making)
• Frontal lobe - motor


  • Frontal Eye Field (Anterior to premotor cortex, voluntary eye movement)
  • Broca's Area (Voluntary speech production, left hemisphere - lateral frontal lobe, if damaged leads to expressive aphasia)