Nervous system

Sensory information (stimuli) gathered from inside and outside of body. -Many kinds of sensory information, including pain, pressure, temperature, chemical levels. Sensory input delivered to CNS via peripheral nerves. Sensory nerve fibres are also called afferent fibres. Sensory information travels from peripheral nervous system towards CNS.

Motor division of peripheral nervous system carries impulses away from central nervous system, usually to effector organs. * Motor nerve fibres also called efferent fibres. * There are two types of motor information. Motor information to the somatic nervous system or to autonomic nervous system

Somatic Nervous System * Under voluntary control and effector tissue is skeletal (voluntary) muscle. * CNS response to sensory information may be to activate the somatic nervous system, eliciting a voluntary response involving skeletal muscle movement e.g., if sensory system says you are too hot you may activate your muscle to take off a coat..– this is the motor response that involves the somatic nervous system. It is a voluntary activity that the person chooses to do

Autonomic Nervous System * CNS response to sensory information may be to activate autonomic nervous system, leading to an involuntary action. Autonomic nervous system is responsible for involuntary motor responses. The effector may be smooth or cardiac muscle (both involuntary muscles) or a gland. * If your body feels too hot, the involuntary response is to lose heat through the skin by causing vasodilation. Vasodilatation is an example of an involuntary autonomic nervous system response. The individual cannot control this response. * The autonomic nervous system is further divided into the sympathetic (fight or flight) and the parasympathetic (rest and digest) divisions. A fine balance between both divisions is required for the maintenance of homeostasis.

Nervous tissue has two types of cells: neurons and neuroglia. * Neurons provide most of the functions of the nervous system, e.g., sensing, thinking, controlling muscle activity, and regulating glandular secretions. * Neuroglia support, nourish, and protect the neurons and maintain homeostasis in the interstitial fluid that bathes them.

Like muscle cells, neurons (nerve cells) possess electrical excitability, they respond to a stimulus and convert it into an action potential. * A stimulus is any change in environment that is strong enough to initiate an action potential. An action potential or impulse is an electrical signal that propagates (travels) along the surface of the membrane of a neuron or a muscle fiber. * Transmission of the nerve signal is electrical within the nerve, but chemical as it passes from nerve to nerve * Bundles of neurons are called nerves

Cell body contains the nucleus and usual cellular components (mitochondria, ER, Golgi) They receive impulses from other nerves via their dendrites The signal is passed along their axon This is transmitted to other nerves or effector organs via terminal boutons

Groups of cell bodies make up the grey matter * Groups of nerve bodies within the CNS are called nuclei (don’t confuse with nucleus of an individual cell) * Groups of nerve bodies in peripheral nervous system are called ganglia * Groups of axons and dendrites make up the white matter (as there is a lot fat (myelin) around them. They are called tracts in the spinal cord and nerve fibres outside of the CNS

Schwann cells are example of neuroglia Between the thin wrapped- around layers of the Schwann cell is fatty substance; myelin Myelin acts as an insulator Large axons and those of PNS are usually myelinated

At rest, inside of nerve is negatively charged compared to outside. At rest there is more K+ inside the cell than outside When stimulus occurs, Na+ rushes into cell through pores (gates) and charge changes to positive on inside and negative on outside. In a slower response, K+ starts to leave the cell

Depends on whether myelinated = faster * Larger neurone (axon ) = faster * Fastest conduction is about 130 meters /second * Unmyelinated small nerves 0.5 meters/second

Tips of most axon terminals swell into synaptic end bulbs. These bulb-shaped structures contain synaptic vesicles, tiny sacs that store chemicals called neurotransmitters. Release of neurotransmitter is method of communicating with next nerve or effector cell.

Site where two neurons or a neuron and an effector cell communicate is termed a synapse. * The neuron sending the signal is called the presynaptic neuron (pre = before), and neuron receiving the message is called the postsynaptic neuron (post = after). * Although presynaptic and postsynaptic neurons are close together, their plasma membranes do not touch. They are separated by synaptic cleft, a tiny space filled with interstitial fluid.

At a chemical synapse, a presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (neurotransmitter release). The postsynaptic neuron then converts the chemical signal back into an electrical signal (nerve impulse).

Neurotransmitter bind receptor signals to join channels to affect depolarisation

neurotransmitter will continue to affect postsynaptic receptors until it is turned off by being removed from its receptor. Neurotransmitters are removed in three ways: (1) Some neurotransmitter molecules diffuse away from synaptic cleft. (2) Some are destroyed by enzymes. (3) Many neurotransmitters are actively transported back into neuron that released them (reuptake) or transported into neighbouring neuroglia (uptake). -This is important for SSRI antidepressants (selective serotonin reuptake inhibitors)

Consists of a central canal and grey and white matter. * Grey matter consists mostly of cell bodies and their dendrites * Whiter areas consist of the axons of neurones, carrying signals up and down the cord. * These tracts cross to the other side as they enter and exit the brain * Explains why right side of brain controls left side of body and vice versa.

Looks like letter H Grey columns= neuronal cell bodies White columns= tracts of axons relaying messages from or to brain Root ganglia= collection of neuronal cell bodies

Anterior grey columns are neuronal cell bodies of motor neurones that leave cord from anterior root Also contain cell bodies of interneurons that link sensory and motor neurones at spinal cord level Posterior grey columns are cell bodies of sensory neurones that synapse with the sensory nerve coming in from periphery (who have their cell bodies in the posterior root ganglion)

Protected within vertebra Surrounded by fluid (cerebrospinal fluid (CSF), made within brain) Central canal and the layer between spinal meninges contain CSF.

finishes at around L1 nerve roots continues as a cauda equina

A method of communication between brain and the peripheral nerves that leave the spinal cord.it has two major functions in maintaining homeostasis;Tracts of white matter of spinal cord carry sensory impulses to brain and motor impulses from brain to skeletal muscles and other effector muscles. * Grey matter of the spinal cord is a site for integration of reflexes, which is a rapid, involuntary action in relation to a stimulus.

Two main forms Upper motor neurones have cell bodies in brain Axons travel down spinal cord and synapse with lower motor neurones (the final nerves to signal to the muscle) within the anterior spinal cord If you cut a lower motor neurone the muscle will “go floppy” If you cut an upper motor neurone the tone will remain or may even go firmer

Upper motor neurones in brain stem and spinal cord maintain posture and balance * Spinal reflexes are the simplest examples * Involving sensory neurone * Interneurone in spinal cord * Lower motor neurone * Reflex’s are protective mechanisms