Peripheral Nervous System
- The cell bodies of the sensory neurones = in the dorsal root ganglia
- Axons and dendrons enter and leave the spinal cord in spinal nerves
- Cranial nerves - Nerves arising from the brain
- Made up of the Autonomic and Somatic nervous systems.
Somatic Nervous System
Includes all sensory neurones and motor neurones that take info to the skeletal muscles. It is the typical reflex arc
Autonomic Nervous System
- Sends action potentials to all internal organs (viscera)
- Controls both smooth muscle and cardiac muscle
- Controls exocrine glands
- Not under voluntary control
- The cell bodies of the motor neurones of the autonomic nervous system are in autonomic ganglia
- Preganglionic neurones carry action potentials from the central nervous system to the autonomic ganglia.
The Sympathetic and Parasympathetic Nervous System
The autonomic nervous system is made up of the sympathetic and parasympathetic nervous systems.
- Stimulating effect on organs
- Transmitter substance is normally noradrenaline, but can be acetylcholine
- Fight or Flight
- Rest and digest
- Transmitter substance is always acetylcholine
- Nerve pathways begin in the brain, at the top of the spinal cord or at the very base of the spinal cord
- Neurone from the central nervous system connects all the the way to the target tissue
Effects of the autonomic nervous system...
... On the digestive System:
- Parasympathetic stimulates digestive activity - increase salivary and gastric gland output, sphincter muscles open and smooth muscle contracts.
- Sympathetic reduces peristalsis, close sphincters and reduce salivary gland output via vasoconstriction. Food moves slower through digestive system.
...On the heart:
- Sympathetic increases rate and force of contraction
- Parasympathetic slows heart rate
...On the Pupil in the eye:
- Sympathetic - radial muscles contract. Pupil widens
- Parasympathetic - circular muscles contract. Pupil narrows
3 membranes called meninges secrete cerebro-spinal fluid, which fills the ventricles (spaces) in the brain
Capillaries in the brain are less leaky than those around other organs. This is to act as a blood-brain barrier to prevent potentially damaging substances entering the blood.
- Involved in movement and posture
- Receives impulses from eyes, ears, muscles and joints
- Used to coordinate the time and pattern of skeletal muscle contraction, so movements are fluid.
Medulla Oblongata: Controls non-skeletal muscles and forms a link between the brain and the spinal cord. The Medulla oblongata coordinates involuntary movements such as breathing.
Made of 2 cerebral hemispheres connected by the Corpus Callosum
Left hemisphere - receives info from right side of body and vice versa.
Information first arrives at primary sensory areas. Nerve impulses are then sent to association areas. At motor areas, nerve impulses are made and sent to effectors.
Limbic System - An association area concerned with emotions and memory. It contains the hippocampus (memory) and amygdala (emotions, autonomic and endocrine systems). Association areas on the left = language.
- Broca's Area - Speech production.
- Wernicke's Area - Speech comprehension
Right hemisphere = non-verbal processes such as visualising 3-D and recognising faces.
Structure of Skeletal muscles
- Muscle fibres - Bundles of long cells
- Cell membrane of muscle fibre cells is called the sarcolemma
- T tubules - bits of the sarcolemma folded inwards into sarcoplasm. Help spread electrical impulses, so all muscle fibres are reached.
- Sarcoplasmic reticulum - internal membranes the store/release Ca ions.
- Lots of mitochondria
- Lots of myofibrils -organelles made of protein and specialised for contraction
- Myofibrils are made of filaments - actin and myosin
Actin - Globular protein. An actin filament is 2 actin molecules twisted together. Contains 2 fibrous proteins: troponin and tropomyosin.
Myosin - Fibrous proteins with a tail and 2 heads. Tails are attached to the M line. The Myosin heads act as ATPases.
Sliding filament model
1. At rest, Tropomyosin covers the binding site on the actin filament.
2. Action potential causes troponin and tropomyosin to change shape. The binding site on actin can be bound to by the myosin heads.
3. The Myosin heads tilt, pulling the actin filament and contracting the muscle.
4. Cross bridge between actin and myosin broken by ATP hydrolysis. Myosin heads spring back and attach to the next binding site along.
Specialised synapses where neurones and muscles meet.
- 1. Action potential arrives and causes uptake of Ca ions.
- 2. Ca ions cause acetylcholine vesicles to fuse with presynaptic membrane.
- 3. Acetylcholine diffuses across cleft and binds to receptors in the sarcolemma, opening Na channels.
- 4. Na ions flood into sarcolemma through open channels. The membrane is depolarised and the action potential spreads along the membrane.
- 5. Depolarisation of sarcolemma spreads down T-Tubules.
- 6. Ca channels open and Ca ions diffuse out of the sarcoplasmic reticulum.
- 7. Ca binds to troponin. Tropomyosin also changes shape and the binding sites are exposed to the myosin heads.
ATP for muscle contraction: Aerobic/anaerobic respiration. Creatine phosphate is stored in the cytoplasm. Creatine phosphate recharged or, if unable to be recharged, converted to creatinine and excreted in urine. ADP + Pi = ATP
Creatine + ATP = Creatine Phosphate + ADP
Cardiac muscle and Smooth muscle
- Striated, but with smaller fibres than skeletal muscles.
- One nucleus
- Intercalated discs seperate fibres from each other
- Gap junctions - joining points between cells
- Cells form connections with adjacent cells
- More mitochondria; it must respire aerobically
- Fatty acids used as a respiratory substrate.
- Long and thin Individual cells with their own nucleus
- Contract more slowly and steadily than skeletal and cardiac muscles
- Contraction caused by autonomic nervous sustem or by hormones such as adrenaline and oxytocin.