Physiology and Anatomy 1

• SCN neurons contain intrinsic clocks, with approximately 24h period 
• Hypothalamic sleep-wake slow pacemaker (24h): SCN neurons orchestrate the whole body 

• Sleep Disorder: Narcolepsy
• Cased by Mutation in the Hypocretin (orexin) 

Bilateral lesions in LH: stop eating, lose weight

Bilateral lesions in VMH: overear, get fat 

Indicators of energy excess activate Appetide-suppressing, body-weight-reducing neurons and vice versa 

• Exist in the hypothalamus
• appetite surpressing neurons
• Reduce food-seeking 
• Work together with Agrp neuons --> in oppsite direction 

• Exist in the hypothalamus
• Appetite increasing neurons 
• Increase food seeking 
• Work together with the POMC cells --> opposite 

• Agrp is necessary for food intake
• Regulated by peripheral hormones such as leptin and ghrelin
• Activated by energy deficit
• Agrp are excited by ghrelin and inhibited by leptin

• causre rare monogenic human obesity 

The hypothalamus senses external and internal signals. 

• Internal signals give mostly feedback information (what is already happenisch in the body) 
• External signals are ofter used to guess what is probable in the future

The hypothalamus controls almost everything based on these external and internal signals: body hormone release, heart-rate, breathing, sleep, eating, running, decision-making. 

The peripheral nervous system is made up of neurons and axons that transmit information between the CNS (center) and the body (periphery)

• To CNS = Sensory = afferent
• From CNS = motor = efferent 

A variety of somatic sensor receptors are found in surface tissues of the body. They are basically axon ending. Their distribution is not even in different body parts. 

• Different sensations travel at different speeds
• Myelin: Impulse accelerator 

Temperature-sensitive nerve endings contain thermosensitive (thermoreceptor TRP) ion channels. These are excitatory channels. 

• TRPV1: senses heat. Capsaicin shifts temperature-sensing of TRPV1 channel to lower temperatures 

Activity of TRPV1-containing nerve endings is coupled to hot percept in CNS --> capsaicin causes heat-like sensation 

• TRPM8: senses cooling. Menthol shifts temperature-sensing of TRPM8 channel to higher temperatures. 

Activity of TRPM8 containing nerve is couples to cool percept in CNS. So menthol causes a cooling like sensation 

Pain sensing nerve endings (nociceptors) don't sense just one physical or chemical signal. They typically sense pressure, temperature and a variety of chemicals indicative of tissue damage. 

Mechanosensitive ion channels in touch receptor nerve endings convert physical deformation into transmembrane excitatory current, producing action potentials travelling to CNS from the touch receptor.

• Each touch receptor is connected to a single axon that carries info to CNS
• Different types of touch receptirs differ in spatial resolution 
• Some body parts are more discerning than others --> fingertips and tongue have as many repectors as 100 per cm²  and the back of the hand less than 10 per cm²

• consists of afferent nerves (sensory nerves) or motor efferent nerves (motor nerves)
• Afferent nerves are responsible for relaying sensation from the body to the CNS
• Efferent nerves are responsible for sending out commands from the CNS to the body (stimulating muscle contractions) --> neurons connected with skeletal muscles and skin
• controls all voluntary muscular systems within the body 

• Postsynaptic is skeletal muscle --> each muscle fiber is innervated by a single axon 
• Nerves emerge from spine roughly at the level of muscles they innervate 
• APs (action potentials) govern muscle contractions -->

1. More APs = more contractions
2. Trains of APs = tonic contraction

1. Motor neuron APs release acetylcholine (ACh) into muscle
2. Ach binds to ACh-gated ion channels on muscle (nicotonic ACh receptors)
3. ACh is degraded in cleft by ACh esterase (AChE) 
4. Ion channels are excitatory, they depolarize and generate muscle AP
5. This causes the calcium concentration to increase in muscle cytosol
6. Calcium makes muscle contract

• Fluctuating muscle weakness
• Eyes dont work together, problems smiling, talking, swallowing
• Normally: Action potential and Tension work together and are constant--> electrical and mechanical response 
• Myasthenia: APs anf Tension not constant --> decrease 
• Body makes antibodies against nicotinic ACh receptors --> some receptors are blocked or damaged by antibodies 
• Treatment: M.G., Dialysis --> AChE inhibitor drugs allow more AChE to hit remaining ACh receptors --> rescue the failing nerve-muscle transmission 

• Is a division of the peripheral nervous system
• Supplies smooth muscle and glands --> influences internal organs 
• Acts largely unconsciously 
• Regulates bodily functions --> heart rate, digestion, respiratory rate, urination 
• regulated by the hypothalamus within the brain
• 3 branches: sympathetic nervous system, parasympathetic nervous system and enteric nervous system 

• Leads to sensory confusion called referred pain. 
• For example: autonomic sensing of physicochemical imbalance in heart may consciously feel like pain in left arm 

• The autonomic nervous system is not under voluntary control --> we can be conscious of some of its outputs
• Parasympathetic = motor ANS = rest and digest = uses mostly acetylcholine
• Sympathetic = motor ANS = fight or flight = uses acetylcholine and noradrenaline 

• Vagus nerve contains molecularly-seperate sensorimotor neurocircuits, each specialised for different things
• Some cells sense intestinal nutrients --> when these cells are stimulate,  stomach expells less food into intestine
• This implies this vagal (ANS) sensorimotor loop: 

Sensory: nutrients --> motor respinse: slow stomach motility

• Other sensorimotor circuit senses stomach strech and induce stomach contraction