Chapter 6B Human Physiology

Central Nervous System Organization

The Nervous System

  • CNS is composed of the brain and spinal cord
  • The PNS has afferent (somatic, visceral, and special) sensory and efferent (somatic and automic motors) seconds
  • Nerve: A group of axons (nerve fibers) traveling together in the PNS
  • Pathway: A group of axons traveling together in the CNS
  • White Matter: The name given to groups of axons as a whole, whether in the PNS or CNS
  • Ganglion: A group of neuron cell bodies in the PNS
  • Nucleus: A group of neuron cell bodies in the CNS
  • Gangions and nulcei are considered grey matter

The Brain

  • Forebrain: The cerebrum and the diencephalon
  • Hindbrain: Pons, medulla, cerabellum
  • Cerebrum, brainstem, diencephalon, cerabellum: Four main parts of the brain
  • Cerebrum: Composed of two hemispheres, makes up the majority of the forebrain
    • Cerebrum: The part of the brain used for perception, skilled movements, learning, and memory
    • The four lobes of the cerebrum are the frontal, parietal, temporal, and occipital
    • frontal, parietal, temporal, and occipital: The four lobes of the cerebrum are the…
    • Cerebral cortex: The outer shell of the cerebrum, made of highly-folded grey matter
    • Corpus callosum: The tract that connects the left and right hemispheres of the cerebrum
    • The corpus callosum is made of white matter
    • Subcortical nuclei: Grey matter deep in the cerebrum
    • Basal nuclei: Deep collections of gray matter in the crebrum that mainly do movement control and posture
  • Diencephalon
    • Thalamus: The synaptic relay center of the brain that integrates afferent inputs to the cerebral cortex, in charge of controling arousal and attention
    • Afferent: The thalamus deals with __________ inputs
    • Hypothalamus: Homeostatic control center of the brain, center for autonomic and endocrine control
    • Epithalamus: Contains pineal gland and plays a role in biological rhythms
  • Brainstem: Contains reticular information in the brain, has three parts
    • Reticular formation is essential for eye movement control, cardiovascular control, breathing, swallowing, sleeping and waking
    • The brainstem is made of the midbrain, pons, and the medulla oblongata
    • Midbrain
    • Pons
    • Medulla Oblongata
  • Cerabellum: Part of the braian, important for coordinating movements, and controlling posture & balance
  • Limbic system: A group of strucutres within the brain that are associated with learning, emotions, and behavior
    • The limbic system is made up of the frontal lobe, temporal lobe, thalamus, and hypothalamus

The Spinal Cord

  • The central core of the spinal cord is made of gray matter (cell bodies and dendrites)
    • Ventral horn: Part of the spinal cord that contains cell bodies for exiting efferent neurons
    • Dorsal horn: Part of the spinal cord where afferent neurons enter the CNS and synapse when they meet their targets
  • The outer layer of white matter on the spinal cord is made up of tracts that lead to the brain
    • Afferent tracks in the spinal cord are considered ascending
    • Efferent tracks in the spinal cord are considered descending

Peripheral Nervous System Organization

Overview

  • Afferent division: sensory information from PNS to CNS (somatic, isceral, special)
  • Efferent division: motor commands from CNS to PNS effectors (somatic & autonomic)
  • Most nerves contain both afferent and efferent neurons
  • The PNS can be subdivided into the somatic branch and the autonomic branch

Somatic Division

  • Somatic divison: The effector organ of this PNS division is skeletal muscle; deals with voluntary movement
    • There is a single neuron between the CNS and the effector (skeletal muscle) in somatic division
  • Acetylcholine: The neurotransmitter of somatic neurons
    • Acetylcholine binds to cholinergic receptors and can only excite skeletal muscle
    • To relax muscles, we have to inhibit generation at the spinal cord

Autonomic Division

  • Autonomic division: Part of the PNS that innerates smooth & cardiac muscle, glands, and GI neurons
  • Autonomic neurons can excite or inhibit effectors
  • Two neurons between the CNS and the effector for autonomic division
    • Preganglionic: The neuron that moves the signal from CNS to autonomic ganglion
    • Preganglionic neuron leaves the spinal cord at the top and bottom of the cord for the parasympathetic branch
    • Postganglionic: Neuron that moves the signal from ganglion to effector
    • Preganglionic neuron leaves the spinal cord in the middle of the cord for the sympathetic branch
  • Autonomic nervous system (ANS) is divided in to the sympathetic and the parasympathetic branches
    • Many autonomic effectors can accept signals from both the symapthetic and parasympathetic branches
    • One branch of the ANS has one effect on the effector, and the other branch has the opposite effect
  • Sympathetic Nervous system: the thoracolumbar division in the ANS
    • Movement of the signal comes from a short pregang neuron, moves into the trunk, and has a long post-gang neuron to the effector for the SNS
    • The sympathetic branch diverges (aka effects multiple tissues at once) much more than the parasympathetic
    • SNS pregangs release Ach which binds to nicotinic receptors
    • Postgangs release norepinepherine to bind to adrenergic in the SNS
    • The sympathetic nervous system is responsible for the fight or flight response
    • Adrenal medulla: part of a gland that sits on the kidney that is a modified postgang fiber that releases epinephrine (a lot) and norepinephrine (some) into the blood
  • Parasympathetic Nervous system: The rest and digest system of the ANS, with craniosacral division
    • Long preganglionic neurons, short postganglionic neurons
    • Parasympathetic nervous system pregang neurons release Ach and bind to nicotinic receptors on the postgangs, but the postgangs release Ach that binds to muscarinic receptors on effectors