Organization of the Nervous System Central Nervous System The brain + the spinal cord The center of integration and control Peripheral Nervous System The nervous system outside of the brain and spinal cord Consists of: 31 Spinal nerves 12 Cranial nerves

Central Nervous System (CNS) contains fluid-filled spaces which contain cerebrospinal fluid (CSF). White matter is composed of bundles of myelinated axons Gray matter consists of unmyelinated axons, nuclei, and dendrites.

Figure 48.16x Spinal cord White Matter Gray Matter

Figure 48.20 The main parts of the human brain

Corpus callosum Midbrain Thalamus Pons Hypothalamus Medulla oblongata This is a slice right down the mid line, mid-saggital. Cut his face off to ensure anonymity. You can see the cerbral cortex on top and the top surface of those sulci and gyri as it dips down the middle, and the cerebellum A striking feature is a big white wodge in the middle - it is white because you have cut right through the middle of a load of myelinated fibres that connect the two hemispheres = corpus callosum Below that the septum pelucidum (but the ventricles are the important bit) - produce CSF Then thalamus - last relay for sensory information before the cortex Hypothalamus - controls the pituitary gland below it Midbrain - start of connection to the spinal cord Pons - lots of fibres connecting the two halves of the cerebellum Brain stem = medulla oblongata - connects to spinal cord In coronal section you see next to nothing in the real slices, so here is Pocock and Richards picture Medulla oblongata

Figure 48.28x1 Brain MRI

But here is a real one.

Mapping Language Areas of the Cerebral Cortex Max Min

Figure 48.27 The limbic system

Structure and Function Brain stem--Consists of the medulla oblongata, pons, and midbrain. Functions in homeostasis, coordination of movement, conduction of impulses to higher brain centers Medulla Oblongata- Breathing, heart and blood vessel activity, swallowing, vomiting, digestion, and relays information to and from higher brain centers Pons- involved in the regulation of visceral activities such as breathing and relays info. to higher brain

Midbrain-integration of sensory information, in the regulation of visual and auditory reflexes, and relays as well Cerebellum Functions to error-check and coordinate motor activities, and perceptual and cognitive factors. Relays sensory information about joints, muscles, sight, and sound to the cerebrum. Coordinates motor commands issued by the cerebrum; maintains posture

Diencephalon: Thalamus- gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except smell), and channels impulses to appropriate part of cerebral cortex for interpretation Hypothalamus- Regulates autonomic activity involved in thermoregulation, hunger, thirst, sexual and mating behavior, etc… part of the limbic system (emotions) The pituitary gland is attached to the hypothalamus

Cerebrum is the most highly evolved structure in the mammalian brain. Functions: interpretation, initiating voluntary movements, storing memory, retrieving memory, reasoning, center for intelligence and personality Corpus Callosum is the major connection between the two hemispheres.

Peripheral Nervous System Responsible for communication btwn the CNS and the rest of the body. Can be divided into: Sensory Division Afferent division Conducts impulses from receptors to the CNS Motor Division Efferent division Conducts impulses from CNS to effectors (muscles/glands)

Simple Nerve Path

Figure 48.3 The knee-jerk reflex

The nervous system of a vertebrate

Diversity in Nervous Systems

Figure 48.1 Overview of a vertebrate nervous system

Motor Efferent Division Can be divided further: Somatic Nervous System VOLUNTARY (generally) Somatic nerve fibers that conduct impulses from the CNS to skeletal muscles Autonomic Nervous System INVOLUNTARY (generally) Conducts impulses from the CNS to smooth muscle, cardiac muscle, and glands.

Autonomic Nervous System

The main roles of the parasympathetic and sympathetic nerves in regulating internal body functions

Structure of a Vertebrate Neuron

Structural Diversity of Neurons

Neurons

Types of Neurons Sensory Neurons afferent; carry impulses to CNS Interneurons link neurons in the CNS Motor Neurons carry impulses away from CNS to effectors such as muscles and glands SUPPORT CELLS Of Nervous System Schwann Cells: peripheral nervous system—produce myelin sheath Oligodendrocytes: CNS; myelinating cell Astrocytes: CNS; form scar tissue, mop up excess ions, etc, induce synapse formation, connect neurons to blood vessels

Schwann Cells

Synaptic Transmission An AP reaches the axon terminal of the presynaptic cell and causes V-gated Ca2+ channels to open. Ca2+ rushes in, binds to regulatory proteins & initiates NT exocytosis. NTs diffuse across the synaptic cleft and then bind to receptors on the postsynaptic membrane and initiate some sort of response on the postsynaptic cell.

A Chemical Synapse

The Major Known Neurotransmitters

Forces Behind Resting Potential Selective Permeability- some molecules pass through membrane more freely than others; ion channels Sodium-Potassium Pump- transports 3 Na out of, 2 K into cell Result: Concentration Gradient Electrical Gradient

The Basis of the Membrane Potential

Molecular Basis of Action Potential – transmission of a signal along an axon Sodium channels open once threshold is reached, influx of sodium Potassium channels open at AP peak; potassium flows out

Propagation of the Action Potential

Graded potentials and the action potential in a neuron

Generating an Impulse polarized membrane: inside is negative relative to the outside under resting conditions due to distribution of ions controlled by Na+/K+ pump that require ATP Nerve impulse starts when the membrane of the nerve depolarizes due to some stimulus, chemical, temp. changes, mechanical, etc…. Depolarization is caused by the influx of Na+ which causes the membrane to become more positive. This starts an action potential, or nerve impulse. They follow the all or none law!!! The membrane will repolarize when K+ leaves the cell setting the membrane back to resting potential or polarized This de and repolarization continues down the nerve until it reaches another nerve to pass on the impulse or until it reaches an effector.

The two hemispheres of the brain are connected by the: What was the substrate in yesterday’s lab? What was the product?

Last Review Questions for the Week: What are the two components of the CNS? What type of response is processed directly in the spinal cord with no impulses traveling to the brain?

Which part of the neuron receives impulses? carries them away? What is the purpose of the myelin sheath?

What is the minimum level of a stimulus required to activate a neuron called? What is meant by the term, “all-or- none principle” with regards to the conduction of nerve impulses?