BI0005 - Lecture 7 - movement in the body
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Movement in the body is everywhere and continuous. There is...
...movement within cells, between cells, and of cells.
There is movement within organs, between organs, and of organs.
Individual muscles move, individual joints move, individual body parts move, and the whole body moves.
What generates movements in the body?
- Molecular motors,
- Molecular motors assembled into large complexes
Briefly, how does skeletal muscle produce a movement of the hand?
- 1. Cross bridges (the molecular motor) form between actin and myosin filaments.
- 2. The relative position of the filaments change
- 3. The sarcomere shortens
- 4. The length of the muscle fibre shortens
- 5. The muscle enters a state of contraction
- 6. The position of the tendon changes
- 7. The movement of the hand follows.
Give 3 examples of molecular motors in situations.
Movement of water in and out of cells - passive diffusion through the plasma membrane - active transport across the plasma membrane by aquaporins.
Ion channels and pumps
Axoplasmic transport - for moving large molecules, organelles, secretory vesicles, and particles around a cell.
What are ion channels?
Ion channels are pore-forming membrane proteins whose functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ionsacross the cell membrane, controlling the flow of ions acrosssecretory and epithelial cells, and regulating cell volume
What are aquaporins?
Aquaporins are integral membrane proteins that form pores in the membrane of biological cells.
What is axoplasmic transport?
Axoplasmic transport, also called axonal transport, is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts (i.e.organelles) to and from a neuron's cell body, through the cytoplasm of its axon (the axoplasm).
What are examples of movement as part of the process of growth?
- Hair growth.
- Growth and remodeling of the skeleton --> change in size and shape.
- Growth of neurones in plasticity.
- These processes are achieved by molecular synthesis.
What are examples of movement between cells?
Intercellular junctions - ions flow between smooth muscle cells and cardiac muscle cells - smooth muscle cells connected by gap junctions.
Synapses in the brain - neurotransmitters are actively transported from the synaptic cleft into the astrocyte
What are examples of movement of cells?
- Unicellular organisms
- Microphages can defend the body because they can move to where they are neeeded, as can microglia in the brain.
Comment on the number of skeletal muscle in the human body
There are 500 skeletal muscles in the body which produce a remarkable combination of motor responses.
Muscles may be described by...
...the direction that the muscle fibers run in.
What is unipennate muscle?
Unipennate muscles have fibres that run the entire length of only one side of a muscle, like a quill pen.
What is bipennate muscle?
- Bipennate muscle consists of two rows of oblique muscle fibres, facing in opposite diagonal directions, converging on a central tendon.
- Stronger than unipennate and fusiform muslce
What are fusiform muscles?
Fusiform muscles have fibres that run parallel to the length of the muscle.
What are motor units?
- They are skeletal muscle fibres innervated by a single motorneurone.
- They are the basis of neuromuscular control
What does the number of muscle fibers in a motor unit depend on?
The number of muscle fibres in a motor unit depends on the activity that an individual muscle has to perform:
Muscles responsible for fine (delicate) movement have small motor units (e.g. hand)
Muscles responsible for coarse (simple) movements have large motor units. (e.g. big muscles of limbs)
All the muscle fibers in a motor unit are...
... of the same fiber type.
Different types of fibres in a muscle can be used depending on need, for example:
- Weak contraction required - only Type 1 fibres activated by motor units.
- Stronger contraction required - Type 2A fibres activated.
- Maximal contraction required - Type 2B fibres activated as well.
How is tension of a muscle produced?
- Tension of a muscle is produced internally by the shortening of myofilaments in the sarcomeres.
- The tension must be transferred to a bone via connective tissues in the muscle itself and the tendon attaching the muscle to the bone.
What are the two primary types of muscle contraction?
Give an examples
Isotonic contraction - tension remains constant as the muscle changes in length
Isometric contraction - Muscle does not shorten and the tension remains at constant muscle length
- For example: lifting and object
- with your hand
- When muscle tension is sufficient
- to overcome the weight of the object in your hand, the muscle shortens, enabling you to lift the object - ISOTONIC
But, if the object is too heavy to lift, the muscle cannot shorten, but still maintain's the tension within it. - ISOMETRIC
Cardiac muscle is...
...striated - the contractile mechanism is the same as skeletal muscle.
Briefly describe the movement of the heart.
- The movement of the heart is different from skeletal muscle as it acts as a pump, moving blood around the body.
- As it has four chambers and the shape of a sac, the mechanics of contraction are very different from those of skeletal muscle.
Contractions of the heart are aided by valves that ensure that the blood is pumped only in one direction: Superior vena cava -> RA -> RV - > LA -> LV -> Aorta.
Briefly comment on the movement of smooth muscle.
Give some examples of smooth muscle movement - 7
- You are usually unaware of the movement of smooth muscles in the body.
- Smooth muscle contractions are very much slower than those of skeletal muscles - seconds rather than milliseconds.
- Contraction of blood vessels to
- assist the circulation
- Contraction of the GI tracts to
- push ingested food along
- Distension of the urinary bladder
- as it fills
Constriction of the pupil
- Contraction of the vas deferens
- during ejaculation of seminal fluid
- Growth and contraction of the
- uterus during pregnancy and birth
- ‘Goose pimples’ in the skin when
- we’re cold
Give examples of the variety of different smooth muscle functions.
- The vas deferens ejects sperm at 50
- metres per second
- The oviduct of a hen pushes the egg
- forward at a speed of a few mm per day
- Arteries can stay contracted for
- many minutes
- The iris constantly changes its
- shape as the light intensity changes
What ever the function – the structure of the smooth muscle cells and their extracellular matrix is the same.
What does the ability of smooth muscles to produce such a wide range of movement, speed of movement, and force of movement depend on?
The ability of smooth muscles to produce such a wide: range of movement, speed of movement and force of movement depends on the spatial arrangement of the smooth muscle cells AND on its nerve supply (innervation)
What is the volume of an empty human bladder?
What is its usual size when emptied?
What is its maximum capacity?
Why doesn't the bladder burst when it is so full?
- Is is due to the structural relationship between the smooth muscle cells and the extracellular components.
- This isn't fully understood.
What is a major difference between skeletal and smooth muscle contractions?
Skeletal muscles are attached to tendons and bones and the contractile force produced by the muscle is transmitted to these skeletal structures to produce movements of the body.
Smooth muscles are not attached to any 'skeletal' structures, only to other parts of the organ they occur in. The hardening of smooth muscles as they contract acts like a supporting skeleton over which the rest of the muscle can move
What is hypertrophy?
Give an example.
- Hypertrophy is increase in cell size
- Smooth muscle cells undergo hypertrophy in response to pressure.
- E.g. The uterus during pregnancy.
- Hypertrophy of the smooth muscle cells in the wall of the uterus and hypertrophy of the smooth muscle cells in the uterine artery.
After birth, everything returns to normal.
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