Nervous system

• Central Nervous System (CNS) consists of the brain and spinal cord
• Peripheral Nervous System (PNS) is responsible for motor control
• Nerves are bundles of axons running through the PNS
• Nucleus refers to a bunch of cell bodies in the CNS
• Ganglion is a group of cell bodies in the PNS
• Somatic nervous system is voluntary while the autonomic nervous system is involuntary
• The nervous system functions to maintain homeostasis
• Sensory input is known as afferent, while motor output is efferent
• Integration functions to decide what to do with the information received
• The neuron consists of:

  • Cell Body transmitting signals
  • Nucleus
  • Nissl bodies (rough ER structured)
  • Dendrite (antenna-like structure)
  • Axon for transmitting signals from the cell body to the terminal in a one-way direction
  • Axonal Hillock where the axon begins
  • Nodes of Ranvier
  • Axonal terminal
• Most motor neurons have branches to communicate with many others simultaneously
• Sensory neurons have the cell body in the middle but still transmit signals in only one direction
• The axon of a neuron is covered in Schwann cells, with a space called nodes of Ranvier between them
• The thicker the myelin sheath, the faster the signal travels, with thickness varying
• The inner ear is a liquid-filled structure containing the cochlea, semicircular canals, and vestibule
• Two types of liquid in the inner ear:

  • Bony labyrinth contains perilymph
  • Membranous labyrinth contains endolymph
• The cochlea, a coiled tube in the ear, functions in hearing
• Organ of Corti (spiral organ) is the functional unit of hearing, where mechanical waves enter the cochlea through the oval window and displace through the round window
• The vestibule, between the cochlea and semicircular canals, functions in static equilibrium and contains the utricle and saccule which house sensory areas called macula (otolith organ)
• The utricle macula responds to horizontal acceleration, while the saccular macula responds to vertical acceleration
• Semicircular canals, with 3 loops in a group, function in dynamic equilibrium with the crista ampullaris as the functional organ
• Impulses sent to the CNS from the inner ear allow us to maintain balance and visually track
• Impulses carried via cranial nerve VIII in the ear function in communication and protection
• The external ear includes the auricle (pinna) with protective hairs and the product of the ceruminous gland
• The middle ear, starting at the tympanic membrane (eardrum), contains auditory ossicles (malleus, incus, stapes) that bridge the eardrum to the cochlea
• The middle ear also has 2 muscles for the attenuation reflex: stapedius and tensor tympani
• Cutaneous sensations include touch, pressure, heat, cold, and pain, traveling from the periphery to the brain via the spinothalamic tract
• Tactile receptors include free nerve endings, hair plexus, Merkel disks, Ruffini corpuscles, Pacinian corpuscles, Meissner's corpuscles, and bulbs of Krause
• Temperature receptors, thermoreceptors, detect temperature changes with specific receptors for heat and cold
• Mechanoreceptors detect forces deforming the receptor, including proprioceptors, baroreceptors, and stretch receptors
• Photoreceptors detect light, while chemoreceptors detect changes in chemical composition
• Sensory adaptation includes tonic receptors adapting slowly to stimuli and phasic receptors adapting quickly
• The Law of Specific Nerve Energy states that receptors receive specific stimuli called "adequate stimuli," such as photoreceptors for light
• Steps to sensation involve stimulation of the receptor, transduction of stimulus into a nerve impulse, conduction of action potential to the CNS, and perception where the brain interprets action potentials
• A generator potential is a graded response in a sensory receptor to a stimulus, generating an action potential as the stimulus strength increases
• The afferent (sensory) system includes somatic and visceral categories of receptors, with exteroceptors detecting stimuli on the body's surface and interoceptors detecting internal stimuli
• Chemoreceptors detect changes in chemical composition, while nociceptors detect damage of a physical, chemical, or thermal nature
• Nicotinic receptors in postganglionic cells always excite ligand-gated channels, opening a Na+ channel leading to depolarization
• Organs with dual innervation include most visceral organs, where antagonistic effects counteract each other
• Most target tissues have dual innervation (both sympathetic and parasympathetic) producing similar effects, while cooperative actions work together to produce a desired effect