Neurophysiology II

• Autonomic Nervous System

  - Involuntary control of visceral effectors

  • Motor neurons of CNS synapse on visceral motor neurons in autonomic ganglia

  • Smooth muscle, glands, cardiac muscle, adipocytes

  - Hypothalamus contains integrative centers

  • Neurons comparable to upper motor neurons in SNS

  • Operates without conscious instruction

  • Coordinates cardiovascular, respiratory, digestive, urinary, and reproductive functions

  - Higher-order functions

   • Consciousness, Learning, Intelligence
• Autonomic Nervous System

  - Visceral motor neurons

  • Preganglionic neurons in brainstem and spinal cord

  • Preganglionic fibers — axons of preganglionic neurons

  - After leaving CNS, they synapse on ganglionic neurons (postganglionic neurons)

  • Autonomic ganglia

  - Contain many ganglionic neurons that innervate visceral effectors (messaging, control, receipt control)

  - Postganglionic fibers — axons of ganglionic neurons (messages pass through these axons to fibers through neurons into CNS)
• ANS

  - 2 divisions of ANS

  • Sympathetic division
  • “Fight or flight”
  • Prepares the body to deal with emergencies
  • Increases alertness, metabolic rate, and muscular abilities
  • Parasympathetic division
  • “Rest and digest”
  • Conserves energy and maintains resting metabolic rate
• Sympathetic and parasympathetic divisions 

  - Usually have opposing effects

  • If sympathetic division causes excitation, the parasympathetic causes inhibition

  - May also work independently

  • Only one division innervates some structures

  - May work together, with each controlling one stage of a complex process
• Responses to increased sympathetic activity

  1. Heightened mental alertness
  2. Increased metabolic rate
  3. Reduced digestive and urinary functions
  4. Activation of energy reserves
  5. Increased respiratory rate and dilation of respiratory passageways
  6. Increased heart rate and blood pressure
  7. Activation of sweat glands
• Responses to increased parasympathetic activity

  1. Decreased metabolic rate
  2. Decreased heart rate and bloodpressure
  3. Increased secretion by salivary and digestive glands
  4. Increased motility and blood flow in digestive tract
  5. Stimulation of urination and defecation
• Sympathetic Division (thoracolumbar division)

  • Short preganglionic fibers in thoracic and lumbar segments of spinal cord
  • Preganglionic neurons located between segments T1 and L2 (damage)
  • Cell bodies in lateral horns
  • Axons enter anterior roots
  • Ganglionic neurons in ganglia near spinal cord
  • Long postganglionic fibers to target organs
• Sympathetic Chain Ganglion

  - located on either side of the vertebral column, serves both side of body

  - CNS preganglionic (short) to ganglion to postganglionic fiber outside CNS in peripheral nervous system to effector (long)

  - one preganglionic fiber synapses on many ganglionic neurons fibers interconnect symapthetic chain ganglia

  • looks like chain of pearls

  • each ganglion innervates a particular body organ or group of organs

  - ganglion neurons synapse in 3 locations: sympathetic chain, collateral ganglia, and adrenal medulla
• Sympathetic Chain vs Collateral Ganglia

  - innervates visceral effectors by spinal nerves, visceral organs in thoracic cavity, body wall, head, neck, and limbs

  - preganglionic fibers synapse on ganglionic fiber to postganglionic fibers

  VS

  - innervates visceral organs in abdominopelvic cavity

  - preganglionic fibers synapse on collateral ganglia to postganglionic fibers
• Adrenal Medulla

  - Center of each adrenal gland

  - Modified sympathetic ganglion at center of each adrenal gland

  - Innervated by preganglionic fibers that synapse on cells that secrete

  • Epinephrine (adrenaline)

  • Norepinephrine (noradrenaline)

  - Bloodstream carries neurotransmitters throughout body

  - Causes changes in metabolic activities of different cells

  • Including cells not innervated by sympathetic postganglionic fibers

  - Effects last much longer than those produced by direct sympathetic innervation

  • Hormones continue to diffuse out of bloodstream
• Sympathetic activation

  - The sympathetic division can change the activities of specific effectors

  • Sympathetic activation
  • Occurs during a crisis
  • The entire division responds
  • Controlled by sympathetic centers in hypothalamus
  • Affects peripheral tissues and CNS activity
• Sympathetic Activation

  - Changes caused by sympathetic activation

  • Increased alertness
  • Feelings of energy and euphoria
  • Increased blood pressure, heart rate, breathing rate, and depth of respiration
  • Elevation in muscle tone
  • Mobilization of energy reserves
• Sympathetic Activation

  - Stimulation of sympathetic preganglionic neurons

  • Releases acetylcholine (ACh) at synapses with ganglionic neurons

  • Effect is always excitatory

  - Ganglionic neurons

  • Release neurotransmitters at target organs, multiple target cells for organs to respond quickly

  • Telodendria form branching networks

  • Each swollen segment is a varicosity

  - Packed with neurotransmitter vesicles

  - Membrane receptors scattered across target cells
• Parasympathetic division (craniosacral division)

  - Long preganglionic fibers in brainstem and sacral segments of spinal cord

  • Autonomic nuclei are in all parts of brainstem and lateral horns of S2–S4

  - Ganglionic neurons in peripheral ganglia within or adjacent to target organs

  - Short postganglionic fibers in or near target organs
• Parasympathetic division

  - Ganglionic neurons in peripheral ganglia

  • Terminal ganglion

  - Near target organ

  - Usually paired

  • Intramural ganglion

  - Embedded in tissues of target organ

  - Consists of interconnected masses and clusters of ganglion cells, activates organs quicker
• Organization of parasympathetic division

  • Parasympathetic preganglionic fibers leave brain in cranial nerves
  • III (oculomotor)
  • VII (facial)
  • IX (glossopharyngeal)
  • X (vagus)
  • Control visceral structures in head
  • other segments go into other organs: kidney, bladder, sex organs
  • Synapse in ciliary, pterygopalatine, submandibular, and otic ganglia
• Major effects of parasympathetic division

  • Constriction of pupils and focusing on near objects
  • Secretion by digestive glands
  • Absorption and use of nutrients by peripheral cells
  • Changes associated with sexual arousal
  • Increased smooth muscle activity in digestive tract
  • Stimulation and coordination of defecation
  • Contraction of urinary bladder during urination
  • Constriction of respiratory passageways
  • Reduction in heart rate and force of contraction
• Sympathetic division has widespread effects

  • 2 sets of sympathetic chain ganglia, 3 collateral ganglia, and 2 adrenal medullae
  • Short preganglionic fibers, long postganglionic fibers
  • Extensive divergence
  • Preganglionic neurons release ACh; most postganglionic fibers release NE
  • Effector response depends on second messengers
• Parasympathetic division has specific effects

  • Visceral motor nuclei are associated with cranial nerves III, VII, IX, and X, and with S2–S4
  • Ganglionic neurons are located in ganglia within or next to target organs
  • Innervates regions serviced by cranial nerves and organs in thoracic and abdominopelvic cavities
  • 1/5 the divergence of sympathetic division
  • All neurons are cholinergic
  • Effects are generally brief and restricted
• Sympathetic vs Parasympathetic

  - Sympathetic: short preganglionic fibres in CNS - ganglionic neuron - long postganglionic fibers to target organ or into blood stream

  • thoracolumbar: T1-L2

  - Parasympathetic: long preganglionic fibres in CNS - ganglionic neuron near or in target organ - short postganglionic fibers

  • cranial sacral: cranial nerves to S2-S4

  
• Dual innervation

  • Most vital organs are innervated by both divisions of ANS

  • Two divisions commonly have opposing effects

  • Parasympathetic postganglionic fibers travel by cranial nerves to peripheral destinations

  • Sympathetic innervation reaches same structures

  • From superior cervical ganglia of sympathetic chain
• Plexus innervation

  - Cardiac and Pulmonary Plexus: have both sympathetic and parasympathetic

  - Celiac plecus and ganglion: have both sympathetic and parasympathetic

  - hypogastric plexus: parasympathetic outflow of pelvic nerve and sympathetic postganglionic fibers from mesenteric ganglion
• Somatic Nervous System

  - Controls contractions of skeletal muscles

  - Sensory or Motor pathways

  - Somatic motor pathways

  • Always involve at least two motor neurons

  - Upper motor neuron

  - Lower motor neuron
• Lower motor neuron

  - Cell body lies in a nucleus of brainstem or spinal cord

  • Only the axon extends outside CNS

  - Innervates a single motor unit in a skeletal muscle

  - Activation triggers a contraction in innervated muscle

  - Damage eliminates voluntary and reflex control over innervated motor unit
• Upper motor neuron

  - Cell body lies in a CNS processing center

  - Synapses on lower motor neuron

  - Activity may facilitate or inhibit lower motor neuron
• Conscious and subconscious motor are controlled by:

  - corticospinal pathway

  - lateral pathway

  - medial pathway
• Corticospinal pathway

  - Motor homunculus

  • Functional map of primary motor cortex

  • Corresponds with specific regions of the body

  • Indicates degree of fine motor control available

  - Hands, face, and tongue appear large

  - Trunk is relatively small

  • Proportions are similar to those of sensory homunculus
• Corticospinal pathway

  - Centers in cerebrum, diencephalon, and brainstem

  • May issue somatic motor commands in response to subconscious processing

  • Medial pathway

  - Helps control gross movements of trunk

  and proximal limb muscles

   • Lateral pathway

  - Helps control distal limb muscles that perform precise movements
• Medial pathway

  • Controls muscle tone and gross movements of neck, trunk, and proximal limb muscles**
  • Upper motor neurons are located in
  • Vestibular nuclei
  • Superior and inferior colliculi
  • Reticular formation
  • Upper motor descend into tectospinal tracts, receive auditory sensations and visual sensations
• Lateral pathway

  • Controls muscle tone and precise movements of distal parts of limbs **
  • Axons of upper motor neurons in red nuclei decussate in brain
  • Descend into spinal cord in rubrospinal tracts
• Sensory Pathways

  - Series of neurons that relays sensory information from receptors to CNS

  • Sensory receptors
  • Specialized cells or cell processes that monitor specific conditions in the body or external environment
  • When stimulated, a receptor generates action potentials that are sent along sensory pathways
• Afferent vs Efferent

  - Afferent division of nervous system

  • Somatic and visceral sensory pathways

  - Efferent division of nervous system

   • Somatic motor portion

  - Carries out somatic motor commands that control peripheral effectors

  - Commands travel from motor centers in brain along somatic motor pathways
• Overview of sensory and motor pathways

  - depolarization of sensory receptors - action potential generation - propagation

  - CNS processing, information may be distributed

  - Motor pathway, involuntary: immediate reflex response maybe even before sensations reach cerebral cortex

  - Motor pathway, voluntary: only about 1% are related to consciousness, response can be moderate, enhanced, or supplemented
• Sensory receptors

  - Processes of specialized sensory neurons or cells monitored by sensory neurons

  - Sensation

  • Arriving information

  - Perception

  • Conscious awareness of a sensation
• General senses

  • Describe our sensitivity
  • Temperature
  • Pain
  • Touch
  • Pressure
  • Vibration
  • Proprioception (body position)
• Special senses

  - Olfaction (smell)

  - Gustation (taste)

  - Vision (sight)

  - Equilibrium (balance)

  - Hearing
• Special sensory receptors

  • Provide sensations of special senses
  • Located in sense organs such as the eye or ear
  • Protected by surrounding tissues
• Interpretation of sensory information

  • very little make it to consciousness
  • Stimulus reaches cortical neurons via labeled line
  • Each labeled line carries information about one modality, or type of stimulus (e.g., touch or light)
  • Frequency and pattern of action potentials contain information
  • About strength, duration, and variation of stimulus
  • Your perception of the nature of a stimulus
  • Depends on the path it takes in CNS
• Detection of stimuli

  - Receptor specificity

  • Each receptor has a characteristic sensitivity

  - Receptive field

  • Area monitored by a single receptor cell

  • The larger the receptive field, the more difficult it is to localize a stimulus

  - Transduction

  • Conversion of an arriving stimulus into an action potential by a sensory receptor
• General sensory receptors

  - Divided into four types by nature of stimulus

  • Nociceptors (pain)
  • Thermoreceptors (temperature)
  • Mechanoreceptors (physical distortion)
  • Chemoreceptors (chemical concentration)