1. Cells of the NS

Neurons are made up of the following

- Cell body or Soma this contains the nucleus, the neuron's intracellular organelles (such as the mitochondria and golgi apparatus) and it is the location for cellular metabolism. It is also contains the Nissl Substance. - Dendrites these originate from the soma and extend outwards. They transmit signals they receive from other neurons to the soma. - Axon It arises from the soma from an area called the axon hillock, where action potentials are initiated. The action potentials are conducted through the axon to the axon terminal. Schwann cells - These insulate the axon which aids with rapid transmission of action potentials through the axon. - Axon terminal Distally the axon branches to form axon terminals. These make synaptic connection with other neurons. They contain various neurotransmitters which is released into the synapse to allow signals to be transmitted from one neuron to the next. - Dendritic Spine The small protrusions found on dendrites that are, for many synapses, the postsynaptic contact site.

Dendritic Spines

A dendrite (tree branch) is where a neuron receives input from other cells. Dendrites branch as they move towards their tips, just like tree branches do, and they even have leaf-like structures on them called spines. The more dendritic spines there are the more modulation of other neurons can occur.

myelin

A fatty substance surrounding some neurons. It is what makes your brain's white matter white. Myelin acts as a form of insulation for axons, helping to send their signals over long distances. For this reason, myelin is mostly found in neurons that connect different brain regions, rather than in the neurons whose axons remain in the local region.

Key neurotransmitters: Histamine

A monoamine, plays a role in metabolism, temperature control, regulating various hormones, and controlling the sleep-wake cycle, amongst other functions.Histamine is an excitatory neurotransmitter produced by neurons of the hypothalamus, cells of the stomach mucosa, mast cells, and basophils in the blood. In the central nervous system, it is important for wakefulness, blood pressure, pain, and sexual behavior. In the stomach, it increases the acidity. Key facts: - Excitatory - Released from Hypothalamus, cells of the stomach mucosa, mast cells, and basophils in the blood - Regulates wakefulness, blood pressure, pain, and sexual behavior; increases the acidity of the stomach; mediates inflammatory reactions

Key neurotransmitters: Serotonin (5-HT)

Also a monoamine neurotransmitter. Is an inhibitory neurotransmitter. Functions such as sleep, memory, appetite, and mood.It is also produced in the gastrointestinal tract in response to food. It is secreted by the neurons of the brainstem and by neurons that innervate the gastrointestinal tract (enteric nervous system). Is also found in platelets (thrombocytes) which release it during coagulation (hemostasis). Key facts - Inhibitory - Released from Neurons of the brainstem and gastrointestinal tract, platelets - Functions to regulate body temperature, perception of pain, emotions, and sleep cycle An insufficient secretion of serotonin may result in decreased immune system function, as well as a range of emotional disorders like depression, anger control problems, obsessive-compulsive disorder, and even suicidal tendencies.

Disorders associated with neurotransmitters

Alzheimer's disease: neurodegenerative disorder. associated with lack of acetylcholine in certain regions of the brain Depression: depletion of norepinephrine, serotonin and dopamine in the CNS Schizophrenia: involves excessive amounts of dopamine in the frontal lobes. drugs that block dopamine used to help Parkinson's disease: destruction of substantia nigra, only CNS source of dopamine Epilepsy: lack of inhibitory nts. eg GABA, or increase of excitatory nts eg glutamate Huntington's disease: chronic reduction of GABA. inherited Myasthenia gravis: autoimmune disease. impairment of acetylcholine

CNS cells: Interneurons

As the name suggests, interneurons are the ones in between - they connect spinal motor and sensory neurons. As well as transferring signals between sensory and motor neurons, interneurons can also communicate with each other, forming circuits of various complexity. They are multipolar, just like motor neurons.

Glial Cells: Astrocytes

Astrocytes are star-shaped glial cells within the brain and spinal cord. They make up between 20 and 40% of all glial cells. They have numerous functions, including: - Providing metabolic support The brain has a constant requirement for nutrients such glucose but they are unable to store or produce glycogen themselves. This is overcome by the fact that astrocytes store glycogen which can be broken down to glucose to provide fuel for neurons. Astrocytes can also store lactate which is useful as a fuel during periods of high energy consumption or ischaemia. - Regulating the extracellular ionic environment High-level of ions such as potassium can result in spontaneous depolarisation of the neuron. Astrocytes, thus, remove excess potassium ions from the extracellular space. - Neurotransmitter uptake Astrocytes contain specific transporters for several neurotransmitters such as glutamate. Rapid removal of neurotransmitters from the extracellular space is required for normal function of neurons. - Modulating synaptic transmission In some regions of the brain, for example the hippocampus, astrocytes release ATP in order to increase production of adenosine, which in turn inhibits synaptic transmission - Promotion of myelination by oligodendrocytes

Glial Cells: Astrocytoma

Astrocytomas are intracranial tumours that are derived from astrocytes and may occur at any age, although more common in males low grade are typically benign, typically in the cerebellum, symptoms relating to balance and coordination grade II tumours have the potential to become malignant. often present with seizures. difficult to remove surgically, frequently recur after treatment

Axons

Each neuron in your brain has one long cable (axon) that snakes away from the main part of the cell. It is where electrical impulses from the neuron travel away to be received by other neurons. Depending on the type of neuron, axons greatly vary in length - many are just a millimetre or so, but the longest ones, such as those that go from the brain down the spinal cord, can extend for more than a metre to your foot. An axon typically develops side branches called axon collaterals, so that one neuron can send information to several others. These collaterals, just like the roots of a tree, split into smaller extensions called terminal branches. Each of these has a synaptic terminal on the tip.

Neurotransmitters: Excitatory, Inhibitory & Modulatory

Excitatory: promotes the generation of an electrical signal called an Action Potential in the receiving neuron. depends on the receptor is binds to Inhibitory: decrease electrical excitability on the postsynaptic side to prevent the propagation of an AP Modulatory : are not restricted to the synaptic cleft so can affect large #s of neurons at once. also operating over a slower time course than excitatory or inhibitory transmitters also function to alter the strength of trans,ission between neurons by affecting the amount of nt that is produced and released

Key neurotransmitters: GABA

Gamma-Aminobutyric acid (GABA) is the most powerful inhibitory neurotransmitter produced by the neurons of the spinal cord, cerebellum, basal ganglia, and many areas of the cerebral cortex. It is derived from glutamate. Key facts: - Inhibitory - Released from Neurons of the spinal cord, cerebellum, basal ganglia, and many areas of the cerebral cortex - Reduces neuronal excitability throughout the nervous system functions closely related to mood and emotions. when abnormally low can lead to anxiety.

Key neurotransmitters: Glutamate (Glu)

Glutamate is the most common neurotransmitter in the central nervous system; it takes part in the regulation of general excitability of the central nervous system, learning processes, and memory. Glutamate (Glu) is the most powerful excitatory neurotransmitter of the central nervous system which ensures homeostasis with the effects of GABA (an inhibitory neurotransmitter). It is secreted by neurons of the many of the sensory pathways entering the central nervous system, as well as the cerebral cortex. Key facts: - Excitatory - Released from Sensory neurons and cerebral cortex - Regulates central nervous system excitability, learning process, memory Inappropriate glutamate neurotransmission contributes to developing epilepsy and cognitive and affective disorders

Key neurotransmitters: Norepinephrine (NE) (also called Noradrenaline)

Is a monoamine, and is the primary neurotransmitter in the sympathetic nervous system where it works on the activity of various organs in the body to control blood pressure, heart rate, liver function and many other functions. an excitatory neurotransmitter produced by the brainstem, hypothalamus, and adrenal glands and released into the bloodstream. In the brain it increases the level of alertness and wakefulness. Key facts: - Excitatory - Released from Brainstem, hypothalamus, and adrenal glands - Increases the level of alertness and wakefulness, stimulates various processes of the body Norepinephrine has been implicated in mood disorders such as depression and anxiety, in which case its concentration in the body is abnormally low. Abnormally high concentration of it may lead to an impaired sleep cycle

Key neurotransmitters: Dopamine (DA)

Is a monoamine. Regulates, motor control, reward and reinforcement, and motivation. Dopamine (DA) is a neurotransmitter secreted by the neurons of the substantia nigra. It is considered a special type of neurotransmitter because its effects are both excitatory and inhibitory. [+] Key facts: - Both excitatory and inhibitory - Released from Substantia nigra - Inhibits unnecessary movements, inhibits the release of prolactin, and stimulates the secretion of growth hormone Part of the extrapyramidal motor system: dopamine is important for movement coordination by inhibiting unnecessary movements. In the pituitary gland, it inhibits the release of prolactin, and stimulates the secretion of growth hormone.

Key neurotransmitters: Epinephrine (aka adrenaline)

Is an excitatory neurotransmitter produced by the chromaffin cells of the adrenal gland. It prepares the body for the fight-or-flight response. That means that when a person is highly stimulated (fear, anger etc.), extra amounts of epinephrine are released into the bloodstream. Key facts: - Excitatory - Released from Chromaffin cells of the medulla of adrenal gland - Functions in the The fight-or-flight response (increased heart rate, blood pressure, and glucose production) This release of epinephrine increases heart rate, blood pressure, and glucose production from the liver (glycogenolysis). In this way, the nervous and endocrine system prepare the body for dangerous and extreme situations by increasing nutrient supply to key tissues.

Glial Cells: Microglia

Microglial cells make up between 10 and 15% of cells within the brain and are of a mesodermal origin unlike the other glial cells which are of ectodermal origin. These cells are the phagocytic and immunocompetent cells of the nervous system. They are activated in response to tissue damage and have the capability to recognise foreign antigens and initiate phagocytosis to remove foreign material. If needed, microglia are also able to function as antigen presentin

CNS cells: Motor neurons

Motor neurons of the spinal cord are part of the CNS and connect to muscles, glands and organs throughout the body. These neurons transmit impulses from the spinal cord to skeletal and smooth muscles (such as those in your stomach), and so directly control all of our muscle movements. There are in fact two types of motor neurons: those that travel from spinal cord to muscle are called lower motor neurons, whereas those that travel between the brain and spinal cord are called upper motor neurons. Motor neurons have the most common type of 'body plan' for a nerve cell - they are multipolar, each with one axon and several dendrites.

NS neurons and glia

Neurons are responsible for sensing change and communicating with other neurons. Glial cells work to support, nourish, insulate neurons and remove waste products. Glia are non-neuronal cells (i.e. not nerves) of the brain and nervous system. Glia, unlike neurons, cannot generate action potentials but they are very important in maintaining brain health and in disease.

The Power of the Synapse

Neurons can be excitable or inhibitory

The Synapse

Neurons communicate via chemical synapses Neurons communicate through synapses contact points between the axon terminals on one side and dendrites or cell bodies on other neurons. A synapse is a gap of around 20-40 nanometre-wide, electrical signals coming via the axon are converted into chemical signals through the release of neurotransmitters, and then promptly converted back into electricity as information moves from neuron to neuron.

PNS cells

Remember the PNS is made up of the somatic nervous system and the autonomic nervous system (which is further divided into the sympathetic and parasympathetic nervous systems) PNS consists of nerves (axons) (12 cranial nerves and 31 spinal nerves) ganglion (soma of neurons) Peripheral neurons are similar to neurons in the CNS but typically have specialized nerve endings

CNS cells: Sensory neurons

Sensory neurons are the nerve cells that are activated by sensory input from the environment - for example, when you touch a hot surface with your fingertips, the sensory neurons will be the ones firing and sending off signals to the rest of the nervous system about the information they have received. The inputs that activate sensory neurons can be physical or chemical, corresponding to all five of our senses. Thus, a physical input can be things like sound, touch, heat, or light. A chemical input comes from taste or smell, which neurons then send to the brain. Most sensory neurons are pseudounipolar, which means they only have one axon which is split into two branches.

Ependymal cells

The ependyma is the thin lining of the ventricular system of the brain and spinal cord. This lining is made up of ependymal cells, the basal membranes of which are attached to astrocytes. The main function of these cells is the production of cerebrospinal fluid (CSF) as a part of the choroid plexus. Their apical surfaces are covered with cilia and microvilli, which allow for the circulation and absorption of CSF respectively.

Glial Cells: Oligodendrocytes

These cells are responsible for insulating the axons in the central nervous system. They carry out this function by producing a myelin sheath which wraps around a part of the axon. A single oligodendrocyte has the capacity to myelinate up to 50 axonal segments. They are equivalent to the Schwann cells in the peripheral nervous system. Oligodendrocytes go through stages of maturation before they are able to form myelin

Glial in the PNS

are a little different than in the CNS Schwann cells: Similar to oligodendrocytes in the central nervous system, Schwann cells myelinate neurons in the peripheral nervous system. Satellite cells: Satellite cells surround neurons in the sensory, sympathetic and parasympathetic ganglia and help regulate the chemical environment. They may also contribute to chronic pain. Enteric glial cells: Enteric glial cells are found in the nerves in the digestive system.

Neurotransmitters

are endogenous chemical messengers. They are the molecules used by the nervous system to transmit messages between neurons, or from neurons to muscles. Communication between two neurons happens in the synaptic cleft. Electrical signals travel along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron. A neurotransmitter influences a neuron in one of three ways: 1) Excitatory 2) Inhibitory 3) Modulatory Most neurotransmitters are either small amine molecules, amino acids, or neuropeptides. There are about a dozen known small-molecule neurotransmitters and more than 100 different neuropeptides. These chemicals and their interactions are involved in countless functions of the nervous system as well as controlling bodily functions.

Key neurotransmitters: Acetylcholine (ACh) in the heart

is an inhibitory nt at the parasympathetic endings of the Vagus Nerve. these inhibit the heart muscle through the cardiac plexus

synapses / synaptic terminal

neurons communicate through synapses contact points between the axon terminals on one side and dendrites or cell bodies on other neuurons a synapse is a gap of around 20-40nanonmetre-wide. electrical signals coming via the axon are converted into chemical signals through the release of neurotransmitters, and the promptly converted back into electricity as info moves from neuron to neuron

PNS function

primary role of the PNS is to connect the CNS to the organs, limbs, and skin The PNS consists of sensory neurons, ganglia (clusters of neurons) and nerves that connect peripheral nerves to the spinal cord.

Key neurotransmitters: Acetylcholine (ACh)

s an excitatory neurotransmitter secreted by motor neurons that innervate muscle cells, basal ganglia, preganglionic neurons of the autonomic nervous system, and postganglionic neurons of the parasympathetic and sympathetic nervous systems. Major role in the peripheral nervous system, where it is released by motor neurons and neurons of the autonomic nervous system. Its main function is to stimulate muscle contraction. In the central nervous system it maintains cognitive function Key facts: - Excitatory in all cases except in the heart (inhibitory) - Regulates the sleep cycle, essential for muscle functioning