NERVOUS

• Functions of the nervous system


  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Maintaining homeostasis
  • Establishing and maintaining mental activity

  
• Central Nervous System (CNS)


  • Consists of the brain and spinal cord
  • Receives, analyzes, integrates and generates
  • Command center of the nervous system

  
• Peripheral Nervous System (PNS)


  • Consists of all the nervous tissue outside the CNS (nerves and ganglia)
  • Carries information about the different tissues of the body to the CNS and carries commands from the CNS that alter body activities

  
• Subdivisions of the Peripheral Nervous System


  • Sensory Division
  • Motor Division

  
• Sensory Division


  • Afferent (toward) division
  • Conducts action potentials from sensory receptors to the CNS
  • Neurons that transmit action potentials from the periphery to the CNS are called sensory neurons

  
• Motor Division


  • Efferent (away) division
  • Conducts action potentials from the CNS to effector organs
  • Neurons that transmit action potentials from the CNS toward the periphery are called motor neurons
• Subdivisions of the Motor Division


  • Somatic Nervous System
  • Autonomic Nervous System

  
• Somatic Nervous System


  • Voluntary
  • Transmits action potentials from the CNS to skeletal muscles

  
• Autonomic Nervous System


  • Involuntary
  • Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
  • Has two divisions: Sympathetic and Parasympathetic
• Cells of the Nervous System


  • Neurons (Nerve Cells)
  • Neuroglia (Glial Cells)

  
• Neurons


  • The functional unit of the nervous system
  • Consist of 3 major parts: Soma (Cell body), Dendrites, Axon
  • Myelin sheaths wrap around the axons of some neurons
• Synapses


  • Sites where nerve impulses are transmitted from one neuron to another, or from one neuron to an effector cell
  • Composed of: Presynaptic axon terminal, Postsynaptic cell membrane, Synaptic cleft
• Resting Membrane Potential


  • Also referred to as steady-state potential
  • Created by passive diffusion of ions through a selectively permeable membrane, producing charge separation (-90mV)
• Action Potential


  • Rapid depolarization (more positive) that occurs on an excitable cell (neurons and muscle cells)
  • Initiated by an electrical event or chemical stimulation that causes increased ion permeability in the cell membrane
• Factors that affect nerve conduction velocity

  • Depends on the diameter of the axon and presence of myelin
  • Faster in axons with large diameter
  • Faster in axons with myelin
  • Slower in axons with smaller diameter
  • Slower in unmyelinated axons
• Classification of Neurons According to Number of Processes


  • Multipolar neurons
  • Bipolar neurons
  • Unipolar or pseudounipolar neurons
  • Anaxonic neurons

  
• Classification of Neurons According to Function


  • Sensory neurons
  • Motor neurons
  • Interneurons

  
• Neuroglia (Glial Cells)


  • Supporting cells of the nervous system
  • Do not conduct action potentials
  • More numerous than neurons (10:1)

  
• Gray Matter


  Unmyelinated axons, cell bodies of neurons and neuroglia
• White Matter


  Myelinated axons, oligodendrocyte and other neuroglia
• Central Nervous System


  • Comprises the brain (cerebrum, cerebellum) and spinal cord
  • Completely covered by connective tissue layers
  • Very little collagen=susceptible to injury
  • Consists of two hemispheres with an outer cortex of gray matter and a central region of white matter

  
• Brain


  • Lies in cranial cavity
  • Continuous with spinal cord through foramen magnum
  • Surrounded by 3 meninges: Dura mater, Arachnoid, Pia Mater
  • CSF surrounds brain in subarachnoid space
• Forebrain (Prosencephalon)


  Telencephalon (Cerebrum) is the largest part of the brain, 7/8 of weight of brain, consists of two cerebral hemispheres connected by corpus callosum, responsible for discriminatory identification and integration of sensor information, memory, reasoning, language, emotional behaviour, and initiation of movement
• Frontal Lobe


  Contains most of the dopamine-sensitive neurons in the cerebral cortex, associated with reward, attention, short-term memory tasks, planning, and motivation, center for motor functions and personality
• Parietal Lobe


  Integrates sensory information from different modalities, particularly spatial sense and navigation, enables regions to map objects perceived visually into body coordinate positions, center for sensory function
• Temporal Lobe


  Involved in retaining visual memories, processing sensory input, comprehending language, storing new memories, feeling and expressing emotion, deriving meaning, contains the hippocampus and plays a key role in the formation of explicit long-term memory, modulated by the amygdala, involved in primary auditory perception such as hearing and holds the primary auditory cortex, center for hearing and olfaction
• Occipital Lobe


  Involved in the sense of sight, lesions in this area can produce hallucinations, visual center
• Insular Lobe


  Involved in receiving and processing and integration of various types of information, including taste sensation, visceral sensation, pain sensation, and vestibular function
• Diencephalon


  Part of the brain between the brainstem and the cerebrum, main components are the thalamus, the epithalamus, and the hypothalamus
• Thalamus


  Relay station, sensory input > spinal cord > brainstem > thalamus (thalamic neurons) > cerebral cortex, also influences mood and registers an unlocalized, uncomfortable perception of pain
• Epithalamus


  Small area superior and posterior to the thalamus, consists of a few small nuclei involved in the emotional and visceral response to odors, and the pineal gland which may influence the onset of puberty and play a role in controlling some long-term cycles that are influenced by the light-dark cycle
• Hypothalamus


  Most inferior part of the diencephalon, contains several small nuclei that are very important in maintaining homeostasis, plays a central role in the control of body temperature, hunger, and thirst, sensations such as sexual pleasure, rage, fear, and relaxation after a meal, "nervous perspiration" in response to stress or hunger as a result of depression, plays a major role in controlling the secretion of hormones from the pituitary gland
• Midbrain (Mesencephalon)


  The smallest region of the brainstem, the dorsal part consists of four mounds called the colliculi, also contains a black nuclear mass called the substantia nigra
• Colliculi


  Superior colliculi are involved in visual reflexes and receive touch and auditory information, inferior colliculi are involved in auditory reflexes
• Hypothalamus


  • Plays a central role in the control of body temperature, hunger, and thirst
  • Involved in sensations such as sexual pleasure, rage, fear, and relaxation after a meal
  • Involved in "nervous perspiration" in response to stress or hunger as a result of depression
• Hypothalamus


  • Has a funnel-shaped stalk, the infundibulum, that extends from the floor of the hypothalamus to the pituitary gland
  • Plays a major role in controlling the secretion of hormones from the pituitary gland
  • Mammillary bodies form externally visible swellings on the posterior portion of the hypothalamus and are involved in emotional responses to odors and in memory
• Midbrain (Mesencephalon)


  • The smallest region of the brainstem, just superior to the pons
  • The dorsal part consists of four mounds called the colliculi
  • Contains a black nuclear mass called the substantia nigra
• Colliculi


  • Superior colliculi are involved in visual reflexes and receive touch and auditory input
  • Inferior colliculi are major relay centers for the auditory nerve pathways in the CNS
• Substantia Nigra


  • Part of the basal nuclei
  • Involved in regulating general body movements
• Hindbrain (Rhombencephalon)


  Consists of the Metencephalon (Cerebellum and Pons)