M81Q1 - Homeostasis 2
The Nervous
System
Nervous System
- allows organisms to take in information from the environment and respond by passing information around the body through a network of neural pathways
- nervous system takes information from receptors, interprets the correct response, and sends messages to effectors.
- nerve impulses along neurons (electricity travels between neurons to deliver information).
- nerve impulses along neurons (electricity travels between neurons to deliver information).
Neurons
- functional units of the nervous system, which carry signals throughout the body.
- B DAMS
- cell Body: main spherical part of neuron, contains nucleus
- Dendrites: branch off cell body, extensions that connect the neuron to other neurons, carry info towards cell body.
- Axon: long, thread-like projection, carry info away from cell body.
- Myelin sheath: coats axon to protect and insulate.
- Synaptic knobs: branches from the end of the axon.
The Endocrine
System
Endocrine System
- a group of glands which secrete hormones
- a hormone is a small chemical which causes a response in another region of the body. produced by glands.
- circulatory is the main system for hormone transport, but lymphatic is also used sometimes.
- hormones diffuse out of glands and into the blood, to be taken around the body by the circulatory system.
- each hormone will only bind to specific receptors for that hormone found on target cells (target tissues contain target cells)
Glands and
Hormones
System Comparison
Nervous
- instantaneously sends electrical impulses
- localised to a specific cell or tissue
- temporary response
Components of the Nervous System
- central nervous system (CNS):
- brain + spinal chord
- gathers information from all over the body and coordinates responses.
- peripheral nervous system (PNS):
- nerves and receptors outside of the CNS
- neurones that connect the CNS to the rest of the body
PNS
- somatic:
- voluntary, conscious portion of nervous system.
- made up of nerves that connect to skin, sensory organs, skeletal muscles.
- processes sensory information that arrives via external stimuli, and controls skeletal muscles which allows voluntary movement.
- autonomic:
- involuntary, unconscious portion of nervous system
- made up of nerves that connect to the cardiac muscle in the heart and the smooth muscle in the organs.
- controls heart rate, digestion, salivation, sweating, pupil diameter, etc.
Autonomic Modes Based on Stress Levels:
- parasympathetic:
- calm and relaxed
- nervous system realises you're not in danger and releases neurotransmitter called acetylcholine.
- heart slows to normal, digestive system continues to digest food.
- sympathetic:
- stressed
- nervous system realises you're in danger and releases adrenaline
- adrenaline tells heart to speed up in order to get blood pumping around body so that muscles have better access to oxygen
- digestion is stopped to focus energy towards survival
Types of Neurons
- sensory neuron: carry electrical impulses from receptors to CNS.
- long dendrites to receive sensory info from receptors.
- motor neurons: transmit electrical impulses from CBS to effectors (muscles, organs, glands).
- long axon to send sensory info to effector cells.
- interneurons: transmit electrical impulses between sensory and motor neurons.
- found exclusively in CNS.
- many, short dendrites to carry nerve impulses from sensory neurons to cell body. many, short axons to carry nerve impulses from the cell body to motor neurons.
Endocrine
- slower communication of message to effector.
- hormones can have effects on tissues that are widely distributed around the body.
- a tissue just needs hormone receptors in order to be affected.
- systemic response (cells or tissues throughout the body)
- long-lasting response
- 3 ways for glands to be stimulated and make and release hormones:
- neural stimuli: receiving nerve impulses
- hormonal stimuli: detecting change in the concentration of a hormone
- humoral stimuli: detecting change in the concentration of another substance in the blood.
- response = hormone binds to target cell
- cell's sensitivity to a hormone is linked to number of receptors found on the outside of the cell: lots = dramatic response, few = down-regulated response.
Brain
- Hypothalamus
- controls many metabolic processes, including thermoregulation
- determines whether optimal conditions are being maintained.
- secretes thyrotropin releasing hormone (TRH) > triggers the release of thyroid stimulating hormone (TSH) > causes T3 and T4 to be released.
- produces antidiuretic hormone (ADH) which increased water absorption into the blood from the kidneys.
- Pituitary Gland
- controlled by the hormone secretions of the hypothalamus
- releases several hormones to regulate the secretion of hormones from other glands.
- posterior pituitary gland regulates ADH production.
- anterior pituitary gland regulates production of TSH, growth hormone, FSH.
- Pineal Gland
- secretes melatonin
- control circadian rhythms (24hr bio cycles for eating, sleeping, etc) and regulates reproductive hormones
Thyroid
- controlled by pituitary
- found around neck, alongside parathyroid gland.
- secretes T3 and T4 (involved in thermoregulation)
- parathyroid gland secretes parathyroid hormone, which triggers calcium release into the blood.
Thymus
- responsible for development of immune system
- secretes thymosin, which stimulates the development of T cells
Pancreas
- behind stomach
- controls blood glucose levels
- secretes glucagon and insulin
Adrenal
- help body respond to stress and control blood pressure
- secrete aldosterone (found in adrenal cortex), adrenaline and noradrenaline (found in adrenal medulla)
Gonad
- progesterone and estrogen produced by ovaries
- promote healthy development of female sex characteristics during puberty.
- encourage fertility
- testosterone produced by testes
- involved in masculine development
- both share homeostatic processes like thermoregulation, osmoregulation and glucose homeostasis.